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 $84.83   13.616%   $96.3805   $96.38   $96.40   $96.40  
  Purchase #2 $65.89   8.669%   $71.602   $71.60   $71.60   $71.60  
  Purchase #3 $201.74   4.145%   $210.1021   $210.10   $210.10   $210.10  
  Purchase #4 $46.97   10.235%   $51.7774   $51.78   $51.80   $51.80  
  Purchase #5 $7.86   6.482%   $8.3695   $8.37   $8.35   $8.40  
  Purchase #6 $237.73   4.709%   $248.9247   $248.92   $248.90   $248.90  
  Purchase #7 $144.42   9.382%   $157.9695   $157.97   $157.95   $158.00  
  7 purchase totals = $789.44       $845.1257   $845.12   $845.10   $845.20