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 $92.81   12.427%   $104.3435   $104.34   $104.35   $104.30  
  Purchase #2 $137.81   13.580%   $156.5246   $156.52   $156.50   $156.50  
  Purchase #3 $60.61   6.832%   $64.7509   $64.75   $64.75   $64.80  
  Purchase #4 $134.45   11.472%   $149.8741   $149.87   $149.85   $149.90  
  Purchase #5 $17.73   9.206%   $19.3622   $19.36   $19.35   $19.40  
  Purchase #6 $226.42   3.331%   $233.9621   $233.96   $233.95   $234.00  
  Purchase #7 $105.51   11.171%   $117.2965   $117.30   $117.30   $117.30  
  7 purchase totals = $775.34       $846.1139   $846.10   $846.05   $846.20