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 $176.73   10.105%   $194.5886   $194.59   $194.60   $194.60  
  Purchase #2 $241.37   11.274%   $268.5821   $268.58   $268.60   $268.60  
  Purchase #3 $187.70   11.456%   $209.2029   $209.20   $209.20   $209.20  
  Purchase #4 $131.62   11.162%   $146.3114   $146.31   $146.30   $146.30  
  Purchase #5 $96.36   11.454%   $107.3971   $107.40   $107.40   $107.40  
  Purchase #6 $203.95   7.291%   $218.82   $218.82   $218.80   $218.80  
  Purchase #7 $118.62   4.228%   $123.6353   $123.64   $123.65   $123.60  
  7 purchase totals = $1,156.35       $1,268.5374   $1,268.54   $1,268.55   $1,268.50