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 $189.54   8.686%   $206.0034   $206.00   $206.00   $206.00  
  Purchase #2 $125.62   8.295%   $136.0402   $136.04   $136.05   $136.00  
  Purchase #3 $62.94   6.610%   $67.1003   $67.10   $67.10   $67.10  
  Purchase #4 $75.96   7.267%   $81.48   $81.48   $81.50   $81.50  
  Purchase #5 $209.86   11.438%   $233.8638   $233.86   $233.85   $233.90  
  Purchase #6 $85.77   12.588%   $96.5667   $96.57   $96.55   $96.60  
  Purchase #7 $41.72   10.372%   $46.0472   $46.05   $46.05   $46.00  
  7 purchase totals = $791.41       $867.1016   $867.10   $867.10   $867.10