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 $208.29   8.598%   $226.1988   $226.20   $226.20   $226.20  
  Purchase #2 $123.79   10.527%   $136.8214   $136.82   $136.80   $136.80  
  Purchase #3 $93.55   12.843%   $105.5646   $105.56   $105.55   $105.60  
  Purchase #4 $244.55   9.844%   $268.6235   $268.62   $268.60   $268.60  
  Purchase #5 $92.81   10.748%   $102.7852   $102.79   $102.80   $102.80  
  Purchase #6 $229.62   7.325%   $246.4397   $246.44   $246.45   $246.40  
  Purchase #7 $211.66   12.354%   $237.8085   $237.81   $237.80   $237.80  
  7 purchase totals = $1,204.27       $1,324.2417   $1,324.24   $1,324.20   $1,324.20