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 $205.99   13.867%   $234.5546   $234.55   $234.55   $234.60  
  Purchase #2 $190.63   10.159%   $209.9961   $210.00   $210.00   $210.00  
  Purchase #3 $184.32   11.610%   $205.7196   $205.72   $205.70   $205.70  
  Purchase #4 $17.84   11.338%   $19.8627   $19.86   $19.85   $19.90  
  Purchase #5 $91.57   13.746%   $104.1572   $104.16   $104.15   $104.20  
  Purchase #6 $68.82   9.151%   $75.1177   $75.12   $75.10   $75.10  
  Purchase #7 $197.44   8.461%   $214.1454   $214.15   $214.15   $214.10  
  7 purchase totals = $956.61       $1,063.5533   $1,063.56   $1,063.50   $1,063.60