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 $61.65   7.621%   $66.3483   $66.35   $66.35   $66.30  
  Purchase #2 $218.94   10.738%   $242.4498   $242.45   $242.45   $242.40  
  Purchase #3 $228.60   3.291%   $236.1232   $236.12   $236.10   $236.10  
  Purchase #4 $202.57   9.466%   $221.7453   $221.75   $221.75   $221.70  
  Purchase #5 $208.79   4.774%   $218.7576   $218.76   $218.75   $218.80  
  Purchase #6 $232.91   6.421%   $247.8652   $247.87   $247.85   $247.90  
  Purchase #7 $57.87   6.336%   $61.5366   $61.54   $61.55   $61.50  
  7 purchase totals = $1,211.33       $1,294.8260   $1,294.84   $1,294.80   $1,294.70