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 $95.67   7.629%   $102.9687   $102.97   $102.95   $103.00  
  Purchase #2 $16.95   11.398%   $18.882   $18.88   $18.90   $18.90  
  Purchase #3 $108.31   5.516%   $114.2844   $114.28   $114.30   $114.30  
  Purchase #4 $33.34   5.691%   $35.2374   $35.24   $35.25   $35.20  
  Purchase #5 $66.63   8.830%   $72.5134   $72.51   $72.50   $72.50  
  Purchase #6 $225.32   9.591%   $246.9304   $246.93   $246.95   $246.90  
  Purchase #7 $189.69   6.354%   $201.7429   $201.74   $201.75   $201.70  
  7 purchase totals = $735.91       $792.5592   $792.55   $792.60   $792.50