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 $182.27   8.610%   $197.9634   $197.96   $197.95   $198.00  
  Purchase #2 $133.65   7.478%   $143.6443   $143.64   $143.65   $143.60  
  Purchase #3 $9.69   4.756%   $10.1509   $10.15   $10.15   $10.20  
  Purchase #4 $218.65   9.491%   $239.4021   $239.40   $239.40   $239.40  
  Purchase #5 $246.89   11.739%   $275.8724   $275.87   $275.85   $275.90  
  Purchase #6 $239.26   12.199%   $268.4473   $268.45   $268.45   $268.40  
  Purchase #7 $158.73   7.337%   $170.376   $170.38   $170.40   $170.40  
  7 purchase totals = $1,189.14       $1,305.8564   $1,305.85   $1,305.85   $1,305.90