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 $32.66   8.114%   $35.31   $35.31   $35.30   $35.30  
  Purchase #2 $96.93   11.716%   $108.2863   $108.29   $108.30   $108.30  
  Purchase #3 $93.42   5.359%   $98.4264   $98.43   $98.45   $98.40  
  Purchase #4 $78.61   9.123%   $85.7816   $85.78   $85.80   $85.80  
  Purchase #5 $195.84   8.755%   $212.9858   $212.99   $213.00   $213.00  
  Purchase #6 $11.59   6.708%   $12.3675   $12.37   $12.35   $12.40  
  Purchase #7 $75.32   7.872%   $81.2492   $81.25   $81.25   $81.20  
  7 purchase totals = $584.37       $634.4068   $634.42   $634.45   $634.40