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 $29.91   13.476%   $33.9407   $33.94   $33.95   $33.90  
  Purchase #2 $188.63   10.791%   $208.9851   $208.99   $209.00   $209.00  
  Purchase #3 $191.59   7.706%   $206.3539   $206.35   $206.35   $206.40  
  Purchase #4 $31.39   9.648%   $34.4185   $34.42   $34.40   $34.40  
  Purchase #5 $248.93   4.460%   $260.0323   $260.03   $260.05   $260.00  
  Purchase #6 $66.44   12.831%   $74.9649   $74.96   $74.95   $75.00  
  Purchase #7 $209.49   11.360%   $233.2881   $233.29   $233.30   $233.30  
  7 purchase totals = $966.38       $1,051.9835   $1,051.98   $1,052.00   $1,052.00