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 $215.94   10.213%   $237.994   $237.99   $238.00   $238.00  
  Purchase #2 $31.64   9.314%   $34.5869   $34.59   $34.60   $34.60  
  Purchase #3 $101.34   13.251%   $114.7686   $114.77   $114.75   $114.80  
  Purchase #4 $170.52   12.414%   $191.6884   $191.69   $191.70   $191.70  
  Purchase #5 $100.41   5.497%   $105.9295   $105.93   $105.95   $105.90  
  Purchase #6 $187.53   3.834%   $194.7199   $194.72   $194.70   $194.70  
  Purchase #7 $127.52   13.749%   $145.0527   $145.05   $145.05   $145.10  
  7 purchase totals = $934.90       $1,024.7400   $1,024.74   $1,024.75   $1,024.80