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 $92.98   12.561%   $104.6592   $104.66   $104.65   $104.70  
  Purchase #2 $145.27   4.362%   $151.6067   $151.61   $151.60   $151.60  
  Purchase #3 $69.26   3.740%   $71.8503   $71.85   $71.85   $71.90  
  Purchase #4 $94.43   7.528%   $101.5387   $101.54   $101.55   $101.50  
  Purchase #5 $228.42   7.674%   $245.949   $245.95   $245.95   $245.90  
  Purchase #6 $137.70   5.741%   $145.6054   $145.61   $145.60   $145.60  
  Purchase #7 $120.33   5.341%   $126.7568   $126.76   $126.75   $126.80  
  7 purchase totals = $888.39       $947.9661   $947.98   $947.95   $948.00