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 $98.65   5.277%   $103.8558   $103.86   $103.85   $103.90  
  Purchase #2 $216.71   7.869%   $233.7629   $233.76   $233.75   $233.80  
  Purchase #3 $25.80   5.709%   $27.2729   $27.27   $27.25   $27.30  
  Purchase #4 $175.46   7.673%   $188.923   $188.92   $188.90   $188.90  
  Purchase #5 $123.98   9.181%   $135.3626   $135.36   $135.35   $135.40  
  Purchase #6 $93.59   8.639%   $101.6752   $101.68   $101.70   $101.70  
  Purchase #7 $218.30   3.219%   $225.3271   $225.33   $225.35   $225.30  
  7 purchase totals = $952.49       $1,016.1795   $1,016.18   $1,016.15   $1,016.30