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 $33.83   6.369%   $35.9846   $35.98   $36.00   $36.00  
  Purchase #2 $97.77   3.344%   $101.0394   $101.04   $101.05   $101.00  
  Purchase #3 $110.40   13.732%   $125.5601   $125.56   $125.55   $125.60  
  Purchase #4 $105.56   13.286%   $119.5847   $119.58   $119.60   $119.60  
  Purchase #5 $73.26   12.459%   $82.3875   $82.39   $82.40   $82.40  
  Purchase #6 $51.81   3.299%   $53.5192   $53.52   $53.50   $53.50  
  Purchase #7 $218.77   3.485%   $226.3941   $226.39   $226.40   $226.40  
  7 purchase totals = $691.40       $744.4696   $744.46   $744.50   $744.50