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 $170.71   13.658%   $194.0256   $194.03   $194.05   $194.00  
  Purchase #2 $119.32   13.865%   $135.8637   $135.86   $135.85   $135.90  
  Purchase #3 $100.96   3.666%   $104.6612   $104.66   $104.65   $104.70  
  Purchase #4 $121.43   13.520%   $137.8473   $137.85   $137.85   $137.80  
  Purchase #5 $111.98   4.600%   $117.1311   $117.13   $117.15   $117.10  
  Purchase #6 $56.76   10.499%   $62.7192   $62.72   $62.70   $62.70  
  Purchase #7 $239.66   13.710%   $272.5174   $272.52   $272.50   $272.50  
  7 purchase totals = $920.82       $1,024.7655   $1,024.77   $1,024.75   $1,024.70