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 $58.44   9.801%   $64.1677   $64.17   $64.15   $64.20  
  Purchase #2 $152.75   4.206%   $159.1747   $159.17   $159.15   $159.20  
  Purchase #3 $61.81   3.594%   $64.0315   $64.03   $64.05   $64.00  
  Purchase #4 $177.97   3.754%   $184.651   $184.65   $184.65   $184.70  
  Purchase #5 $91.88   7.113%   $98.4154   $98.42   $98.40   $98.40  
  Purchase #6 $46.58   3.449%   $48.1865   $48.19   $48.20   $48.20  
  Purchase #7 $134.74   3.402%   $139.3239   $139.32   $139.30   $139.30  
  7 purchase totals = $724.17       $757.9507   $757.95   $757.90   $758.00