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 $164.56   11.726%   $183.8563   $183.86   $183.85   $183.90  
  Purchase #2 $232.88   4.234%   $242.7401   $242.74   $242.75   $242.70  
  Purchase #3 $247.76   9.296%   $270.7918   $270.79   $270.80   $270.80  
  Purchase #4 $96.42   6.125%   $102.3257   $102.33   $102.35   $102.30  
  Purchase #5 $180.38   6.568%   $192.2274   $192.23   $192.25   $192.20  
  Purchase #6 $173.84   12.368%   $195.3405   $195.34   $195.35   $195.30  
  Purchase #7 $194.36   11.864%   $217.4189   $217.42   $217.40   $217.40  
  7 purchase totals = $1,290.20       $1,404.7007   $1,404.71   $1,404.75   $1,404.60