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 $55.68   11.185%   $61.9078   $61.91   $61.90   $61.90  
  Purchase #2 $36.34   9.651%   $39.8472   $39.85   $39.85   $39.80  
  Purchase #3 $129.98   4.864%   $136.3022   $136.30   $136.30   $136.30  
  Purchase #4 $30.61   9.428%   $33.4959   $33.50   $33.50   $33.50  
  Purchase #5 $5.63   11.219%   $6.2616   $6.26   $6.25   $6.30  
  Purchase #6 $148.79   8.866%   $161.9817   $161.98   $162.00   $162.00  
  Purchase #7 $242.97   7.871%   $262.0942   $262.09   $262.10   $262.10  
  7 purchase totals = $650.00       $701.8906   $701.89   $701.90   $701.90