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 $234.42   8.761%   $254.9575   $254.96   $254.95   $255.00  
  Purchase #2 $238.68   5.764%   $252.4375   $252.44   $252.45   $252.40  
  Purchase #3 $38.66   8.674%   $42.0134   $42.01   $42.00   $42.00  
  Purchase #4 $116.91   13.498%   $132.6905   $132.69   $132.70   $132.70  
  Purchase #5 $141.35   9.592%   $154.9083   $154.91   $154.90   $154.90  
  Purchase #6 $46.49   6.373%   $49.4528   $49.45   $49.45   $49.50  
  Purchase #7 $13.97   4.277%   $14.5675   $14.57   $14.55   $14.60  
  7 purchase totals = $830.48       $901.0275   $901.03   $901.00   $901.10