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 $117.77   13.462%   $133.6242   $133.62   $133.60   $133.60  
  Purchase #2 $59.67   10.639%   $66.0183   $66.02   $66.00   $66.00  
  Purchase #3 $192.32   11.390%   $214.2252   $214.23   $214.25   $214.20  
  Purchase #4 $173.55   12.194%   $194.7127   $194.71   $194.70   $194.70  
  Purchase #5 $67.59   6.763%   $72.1611   $72.16   $72.15   $72.20  
  Purchase #6 $245.48   6.297%   $260.9379   $260.94   $260.95   $260.90  
  Purchase #7 $76.40   10.196%   $84.1897   $84.19   $84.20   $84.20  
  7 purchase totals = $932.78       $1,025.8691   $1,025.87   $1,025.85   $1,025.80