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 $211.43   11.287%   $235.2941   $235.29   $235.30   $235.30  
  Purchase #2 $162.85   12.149%   $182.6346   $182.63   $182.65   $182.60  
  Purchase #3 $215.64   10.156%   $237.5404   $237.54   $237.55   $237.50  
  Purchase #4 $113.34   12.739%   $127.7784   $127.78   $127.80   $127.80  
  Purchase #5 $228.28   11.826%   $255.2764   $255.28   $255.30   $255.30  
  Purchase #6 $32.60   10.819%   $36.127   $36.13   $36.15   $36.10  
  Purchase #7 $182.92   5.872%   $193.6611   $193.66   $193.65   $193.70  
  7 purchase totals = $1,147.06       $1,268.3120   $1,268.31   $1,268.40   $1,268.30