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 $55.68   12.713%   $62.7586   $62.76   $62.75   $62.80  
  Purchase #2 $62.63   4.233%   $65.2811   $65.28   $65.30   $65.30  
  Purchase #3 $237.70   12.284%   $266.8991   $266.90   $266.90   $266.90  
  Purchase #4 $121.53   7.811%   $131.0227   $131.02   $131.00   $131.00  
  Purchase #5 $93.56   10.862%   $103.7225   $103.72   $103.70   $103.70  
  Purchase #6 $118.61   6.470%   $126.2841   $126.28   $126.30   $126.30  
  Purchase #7 $181.86   6.529%   $193.7336   $193.73   $193.75   $193.70  
  7 purchase totals = $871.57       $949.7017   $949.69   $949.70   $949.70