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 $35.70   9.159%   $38.9698   $38.97   $38.95   $39.00  
  Purchase #2 $116.42   8.107%   $125.8582   $125.86   $125.85   $125.90  
  Purchase #3 $171.26   13.211%   $193.8852   $193.89   $193.90   $193.90  
  Purchase #4 $210.47   11.212%   $234.0679   $234.07   $234.05   $234.10  
  Purchase #5 $91.76   4.697%   $96.07   $96.07   $96.05   $96.10  
  Purchase #6 $248.96   12.118%   $279.129   $279.13   $279.15   $279.10  
  Purchase #7 $205.95   11.129%   $228.8702   $228.87   $228.85   $228.90  
  7 purchase totals = $1,080.52       $1,196.8503   $1,196.86   $1,196.80   $1,197.00