Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $176.59   10.791%   $195.6458   $195.65   $195.65   $195.60  
  Purchase #2 $213.54   11.415%   $237.9156   $237.92   $237.90   $237.90  
  Purchase #3 $107.49   10.185%   $118.4379   $118.44   $118.45   $118.40  
  Purchase #4 $241.54   6.215%   $256.5517   $256.55   $256.55   $256.60  
  Purchase #5 $161.87   7.627%   $174.2158   $174.22   $174.20   $174.20  
  Purchase #6 $231.95   11.646%   $258.9629   $258.96   $258.95   $259.00  
  Purchase #7 $123.55   11.826%   $138.161   $138.16   $138.15   $138.20  
  7 purchase totals = $1,256.53       $1,379.8907   $1,379.90   $1,379.85   $1,379.90