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 $45.71   9.457%   $50.0328   $50.03   $50.05   $50.00  
  Purchase #2 $151.87   11.314%   $169.0526   $169.05   $169.05   $169.10  
  Purchase #3 $143.84   10.484%   $158.9202   $158.92   $158.90   $158.90  
  Purchase #4 $41.38   5.223%   $43.5413   $43.54   $43.55   $43.50  
  Purchase #5 $163.90   7.560%   $176.2908   $176.29   $176.30   $176.30  
  Purchase #6 $187.55   7.582%   $201.77   $201.77   $201.75   $201.80  
  Purchase #7 $229.38   5.492%   $241.9775   $241.98   $242.00   $242.00  
  7 purchase totals = $963.63       $1,041.5852   $1,041.58   $1,041.60   $1,041.60