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 $199.64   9.846%   $219.2966   $219.30   $219.30   $219.30  
  Purchase #2 $41.70   7.136%   $44.6757   $44.68   $44.70   $44.70  
  Purchase #3 $236.58   13.271%   $267.9765   $267.98   $268.00   $268.00  
  Purchase #4 $58.52   5.458%   $61.714   $61.71   $61.70   $61.70  
  Purchase #5 $201.45   7.771%   $217.1047   $217.10   $217.10   $217.10  
  Purchase #6 $207.87   12.785%   $234.4462   $234.45   $234.45   $234.40  
  Purchase #7 $69.55   4.594%   $72.7451   $72.75   $72.75   $72.70  
  7 purchase totals = $1,015.31       $1,117.9588   $1,117.97   $1,118.00   $1,117.90