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 $212.26   6.447%   $225.9444   $225.94   $225.95   $225.90  
  Purchase #2 $83.27   6.583%   $88.7517   $88.75   $88.75   $88.80  
  Purchase #3 $161.77   7.120%   $173.288   $173.29   $173.30   $173.30  
  Purchase #4 $144.31   12.241%   $161.975   $161.98   $162.00   $162.00  
  Purchase #5 $114.66   4.322%   $119.6156   $119.62   $119.60   $119.60  
  Purchase #6 $149.36   6.381%   $158.8907   $158.89   $158.90   $158.90  
  Purchase #7 $106.67   6.436%   $113.5353   $113.54   $113.55   $113.50  
  7 purchase totals = $972.30       $1,042.0007   $1,042.01   $1,042.05   $1,042.00