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 $249.83   4.795%   $261.8093   $261.81   $261.80   $261.80  
  Purchase #2 $79.98   4.608%   $83.6655   $83.67   $83.65   $83.70  
  Purchase #3 $43.37   10.478%   $47.9143   $47.91   $47.90   $47.90  
  Purchase #4 $146.72   7.241%   $157.344   $157.34   $157.35   $157.30  
  Purchase #5 $247.68   6.424%   $263.591   $263.59   $263.60   $263.60  
  Purchase #6 $13.79   10.546%   $15.2443   $15.24   $15.25   $15.20  
  Purchase #7 $92.77   9.763%   $101.8271   $101.83   $101.85   $101.80  
  7 purchase totals = $874.14       $931.3955   $931.39   $931.40   $931.30