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 $249.84   5.626%   $263.896   $263.90   $263.90   $263.90  
  Purchase #2 $45.96   8.103%   $49.6841   $49.68   $49.70   $49.70  
  Purchase #3 $12.32   6.584%   $13.1311   $13.13   $13.15   $13.10  
  Purchase #4 $51.87   5.807%   $54.8821   $54.88   $54.90   $54.90  
  Purchase #5 $144.30   6.632%   $153.87   $153.87   $153.85   $153.90  
  Purchase #6 $176.26   9.140%   $192.3702   $192.37   $192.35   $192.40  
  Purchase #7 $214.65   9.568%   $235.1877   $235.19   $235.20   $235.20  
  7 purchase totals = $895.20       $963.0212   $963.02   $963.05   $963.10