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 $53.39   13.706%   $60.7076   $60.71   $60.70   $60.70  
  Purchase #2 $198.72   12.323%   $223.2083   $223.21   $223.20   $223.20  
  Purchase #3 $217.77   9.797%   $239.1049   $239.10   $239.10   $239.10  
  Purchase #4 $208.30   8.694%   $226.4096   $226.41   $226.40   $226.40  
  Purchase #5 $200.48   9.480%   $219.4855   $219.49   $219.50   $219.50  
  Purchase #6 $46.72   5.551%   $49.3134   $49.31   $49.30   $49.30  
  Purchase #7 $183.43   6.400%   $195.1695   $195.17   $195.15   $195.20  
  7 purchase totals = $1,108.81       $1,213.3988   $1,213.40   $1,213.35   $1,213.40