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 $213.44   11.767%   $238.5555   $238.56   $238.55   $238.60  
  Purchase #2 $120.85   9.639%   $132.4987   $132.50   $132.50   $132.50  
  Purchase #3 $28.30   13.601%   $32.1491   $32.15   $32.15   $32.10  
  Purchase #4 $155.77   3.757%   $161.6223   $161.62   $161.60   $161.60  
  Purchase #5 $155.51   4.143%   $161.9528   $161.95   $161.95   $162.00  
  Purchase #6 $17.31   6.312%   $18.4026   $18.40   $18.40   $18.40  
  Purchase #7 $225.42   11.102%   $250.4461   $250.45   $250.45   $250.40  
  7 purchase totals = $916.60       $995.6271   $995.63   $995.60   $995.60