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 $89.55   13.360%   $101.5139   $101.51   $101.50   $101.50  
  Purchase #2 $151.39   9.663%   $166.0188   $166.02   $166.00   $166.00  
  Purchase #3 $184.49   5.457%   $194.5576   $194.56   $194.55   $194.60  
  Purchase #4 $240.48   5.289%   $253.199   $253.20   $253.20   $253.20  
  Purchase #5 $51.58   3.570%   $53.4214   $53.42   $53.40   $53.40  
  Purchase #6 $245.87   13.772%   $279.7312   $279.73   $279.75   $279.70  
  Purchase #7 $237.77   13.326%   $269.4552   $269.46   $269.45   $269.50  
  7 purchase totals = $1,201.13       $1,317.8971   $1,317.90   $1,317.85   $1,317.90