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 $94.37   10.483%   $104.2628   $104.26   $104.25   $104.30  
  Purchase #2 $124.56   13.326%   $141.1589   $141.16   $141.15   $141.20  
  Purchase #3 $187.64   8.820%   $204.1898   $204.19   $204.20   $204.20  
  Purchase #4 $168.44   10.862%   $186.736   $186.74   $186.75   $186.70  
  Purchase #5 $7.54   5.299%   $7.9395   $7.94   $7.95   $7.90  
  Purchase #6 $195.51   4.499%   $204.306   $204.31   $204.30   $204.30  
  Purchase #7 $123.29   10.829%   $136.6411   $136.64   $136.65   $136.60  
  7 purchase totals = $901.35       $985.2341   $985.24   $985.25   $985.20