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 $53.86   13.536%   $61.1505   $61.15   $61.15   $61.20  
  Purchase #2 $215.41   9.266%   $235.3699   $235.37   $235.35   $235.40  
  Purchase #3 $127.71   5.424%   $134.637   $134.64   $134.65   $134.60  
  Purchase #4 $59.85   5.226%   $62.9778   $62.98   $63.00   $63.00  
  Purchase #5 $100.88   4.141%   $105.0574   $105.06   $105.05   $105.10  
  Purchase #6 $70.68   3.733%   $73.3185   $73.32   $73.30   $73.30  
  Purchase #7 $157.48   9.821%   $172.9461   $172.95   $172.95   $172.90  
  7 purchase totals = $785.87       $845.4572   $845.47   $845.45   $845.50