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 $128.94   9.579%   $141.2912   $141.29   $141.30   $141.30  
  Purchase #2 $118.98   10.778%   $131.8037   $131.80   $131.80   $131.80  
  Purchase #3 $56.42   10.303%   $62.233   $62.23   $62.25   $62.20  
  Purchase #4 $157.99   8.429%   $171.307   $171.31   $171.30   $171.30  
  Purchase #5 $93.43   13.534%   $106.0748   $106.07   $106.05   $106.10  
  Purchase #6 $104.30   9.361%   $114.0635   $114.06   $114.05   $114.10  
  Purchase #7 $68.36   5.314%   $71.9927   $71.99   $72.00   $72.00  
  7 purchase totals = $728.42       $798.7659   $798.75   $798.75   $798.80