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 $43.86   11.727%   $49.0035   $49.00   $49.00   $49.00  
  Purchase #2 $60.59   11.170%   $67.3579   $67.36   $67.35   $67.40  
  Purchase #3 $150.64   9.549%   $165.0246   $165.02   $165.00   $165.00  
  Purchase #4 $32.68   7.452%   $35.1153   $35.12   $35.10   $35.10  
  Purchase #5 $117.26   7.716%   $126.3078   $126.31   $126.30   $126.30  
  Purchase #6 $39.44   6.761%   $42.1065   $42.11   $42.10   $42.10  
  Purchase #7 $118.92   6.158%   $126.2431   $126.24   $126.25   $126.20  
  7 purchase totals = $563.39       $611.1587   $611.16   $611.10   $611.10