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 $197.80   12.749%   $223.0175   $223.02   $223.00   $223.00  
  Purchase #2 $151.49   7.191%   $162.3836   $162.38   $162.40   $162.40  
  Purchase #3 $203.88   6.821%   $217.7867   $217.79   $217.80   $217.80  
  Purchase #4 $151.90   8.672%   $165.0728   $165.07   $165.05   $165.10  
  Purchase #5 $164.74   5.759%   $174.2274   $174.23   $174.25   $174.20  
  Purchase #6 $179.97   6.671%   $191.9758   $191.98   $192.00   $192.00  
  Purchase #7 $175.60   7.835%   $189.3583   $189.36   $189.35   $189.40  
  7 purchase totals = $1,225.38       $1,323.8221   $1,323.83   $1,323.85   $1,323.90