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 $44.83   8.367%   $48.5809   $48.58   $48.60   $48.60  
  Purchase #2 $245.54   4.308%   $256.1179   $256.12   $256.10   $256.10  
  Purchase #3 $205.80   7.302%   $220.8275   $220.83   $220.85   $220.80  
  Purchase #4 $207.96   5.773%   $219.9655   $219.97   $219.95   $220.00  
  Purchase #5 $160.28   7.209%   $171.8346   $171.83   $171.85   $171.80  
  Purchase #6 $14.55   11.433%   $16.2135   $16.21   $16.20   $16.20  
  Purchase #7 $20.86   5.126%   $21.9293   $21.93   $21.95   $21.90  
  7 purchase totals = $899.82       $955.4692   $955.47   $955.50   $955.40