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 $208.88   11.113%   $232.0928   $232.09   $232.10   $232.10  
  Purchase #2 $158.98   5.279%   $167.3726   $167.37   $167.35   $167.40  
  Purchase #3 $243.40   12.414%   $273.6157   $273.62   $273.60   $273.60  
  Purchase #4 $154.26   9.651%   $169.1476   $169.15   $169.15   $169.10  
  Purchase #5 $90.73   6.223%   $96.3761   $96.38   $96.40   $96.40  
  Purchase #6 $238.47   12.518%   $268.3217   $268.32   $268.30   $268.30  
  Purchase #7 $138.97   10.526%   $153.598   $153.60   $153.60   $153.60  
  7 purchase totals = $1,233.69       $1,360.5245   $1,360.53   $1,360.50   $1,360.50