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 $91.72   5.694%   $96.9425   $96.94   $96.95   $96.90  
  Purchase #2 $182.74   5.713%   $193.1799   $193.18   $193.20   $193.20  
  Purchase #3 $249.71   10.813%   $276.7111   $276.71   $276.70   $276.70  
  Purchase #4 $216.44   9.439%   $236.8698   $236.87   $236.85   $236.90  
  Purchase #5 $101.66   4.521%   $106.256   $106.26   $106.25   $106.30  
  Purchase #6 $59.35   4.743%   $62.165   $62.17   $62.15   $62.20  
  Purchase #7 $63.47   6.330%   $67.4877   $67.49   $67.50   $67.50  
  7 purchase totals = $965.09       $1,039.6120   $1,039.62   $1,039.60   $1,039.70