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 $228.68   11.643%   $255.3052   $255.31   $255.30   $255.30  
  Purchase #2 $34.54   4.397%   $36.0587   $36.06   $36.05   $36.10  
  Purchase #3 $214.39   6.347%   $227.9973   $228.00   $228.00   $228.00  
  Purchase #4 $223.39   10.863%   $247.6569   $247.66   $247.65   $247.70  
  Purchase #5 $62.60   10.141%   $68.9483   $68.95   $68.95   $68.90  
  Purchase #6 $55.62   11.157%   $61.8255   $61.83   $61.85   $61.80  
  Purchase #7 $237.51   3.290%   $245.3241   $245.32   $245.30   $245.30  
  7 purchase totals = $1,056.73       $1,143.1160   $1,143.13   $1,143.10   $1,143.10