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 $56.56   13.311%   $64.0887   $64.09   $64.10   $64.10  
  Purchase #2 $130.36   3.113%   $134.4181   $134.42   $134.40   $134.40  
  Purchase #3 $230.94   11.826%   $258.251   $258.25   $258.25   $258.30  
  Purchase #4 $170.93   10.470%   $188.8264   $188.83   $188.85   $188.80  
  Purchase #5 $57.76   6.197%   $61.3394   $61.34   $61.35   $61.30  
  Purchase #6 $88.31   5.175%   $92.88   $92.88   $92.90   $92.90  
  Purchase #7 $84.80   12.225%   $95.1668   $95.17   $95.15   $95.20  
  7 purchase totals = $819.66       $894.9704   $894.98   $895.00   $895.00