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 $60.62   9.360%   $66.294   $66.29   $66.30   $66.30  
  Purchase #2 $48.78   11.194%   $54.2404   $54.24   $54.25   $54.20  
  Purchase #3 $26.99   3.656%   $27.9768   $27.98   $28.00   $28.00  
  Purchase #4 $6.92   11.738%   $7.7323   $7.73   $7.75   $7.70  
  Purchase #5 $144.58   11.718%   $161.5219   $161.52   $161.50   $161.50  
  Purchase #6 $93.53   9.182%   $102.1179   $102.12   $102.10   $102.10  
  Purchase #7 $59.73   5.552%   $63.0462   $63.05   $63.05   $63.00  
  7 purchase totals = $441.15       $482.9295   $482.93   $482.95   $482.80