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 $244.53   7.452%   $262.7524   $262.75   $262.75   $262.80  
  Purchase #2 $145.59   10.859%   $161.3996   $161.40   $161.40   $161.40  
  Purchase #3 $54.96   5.483%   $57.9735   $57.97   $57.95   $58.00  
  Purchase #4 $118.91   12.801%   $134.1317   $134.13   $134.15   $134.10  
  Purchase #5 $159.77   10.172%   $176.0218   $176.02   $176.00   $176.00  
  Purchase #6 $49.62   3.497%   $51.3552   $51.36   $51.35   $51.40  
  Purchase #7 $80.52   12.585%   $90.6534   $90.65   $90.65   $90.70  
  7 purchase totals = $853.90       $934.2876   $934.28   $934.25   $934.40