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 $61.33   9.580%   $67.2054   $67.21   $67.20   $67.20  
  Purchase #2 $113.26   7.678%   $121.9561   $121.96   $121.95   $122.00  
  Purchase #3 $34.50   4.543%   $36.0673   $36.07   $36.05   $36.10  
  Purchase #4 $103.49   6.684%   $110.4073   $110.41   $110.40   $110.40  
  Purchase #5 $188.33   11.119%   $209.2704   $209.27   $209.25   $209.30  
  Purchase #6 $126.82   7.784%   $136.6917   $136.69   $136.70   $136.70  
  Purchase #7 $104.73   5.869%   $110.8766   $110.88   $110.90   $110.90  
  7 purchase totals = $732.46       $792.4748   $792.49   $792.45   $792.60