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 $173.93   12.408%   $195.5112   $195.51   $195.50   $195.50  
  Purchase #2 $50.96   4.738%   $53.3745   $53.37   $53.35   $53.40  
  Purchase #3 $203.50   8.114%   $220.012   $220.01   $220.00   $220.00  
  Purchase #4 $205.92   12.528%   $231.7177   $231.72   $231.70   $231.70  
  Purchase #5 $63.26   11.753%   $70.6949   $70.69   $70.70   $70.70  
  Purchase #6 $126.79   12.796%   $143.014   $143.01   $143.00   $143.00  
  Purchase #7 $107.35   11.248%   $119.4247   $119.42   $119.40   $119.40  
  7 purchase totals = $931.71       $1,033.7490   $1,033.73   $1,033.65   $1,033.70