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 $193.31   5.676%   $204.2823   $204.28   $204.30   $204.30  
  Purchase #2 $216.54   12.368%   $243.3217   $243.32   $243.30   $243.30  
  Purchase #3 $61.33   4.728%   $64.2297   $64.23   $64.25   $64.20  
  Purchase #4 $177.61   13.547%   $201.6708   $201.67   $201.65   $201.70  
  Purchase #5 $47.40   9.176%   $51.7494   $51.75   $51.75   $51.70  
  Purchase #6 $97.95   8.326%   $106.1053   $106.11   $106.10   $106.10  
  Purchase #7 $60.55   7.180%   $64.8975   $64.90   $64.90   $64.90  
  7 purchase totals = $854.69       $936.2567   $936.26   $936.25   $936.20