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 $49.66   12.691%   $55.9624   $55.96   $55.95   $56.00  
  Purchase #2 $5.94   4.246%   $6.1922   $6.19   $6.20   $6.20  
  Purchase #3 $121.63   4.155%   $126.6837   $126.68   $126.70   $126.70  
  Purchase #4 $198.65   8.139%   $214.8181   $214.82   $214.80   $214.80  
  Purchase #5 $9.65   4.262%   $10.0613   $10.06   $10.05   $10.10  
  Purchase #6 $219.42   5.142%   $230.7026   $230.70   $230.70   $230.70  
  Purchase #7 $109.28   8.824%   $118.9229   $118.92   $118.90   $118.90  
  7 purchase totals = $714.23       $763.3432   $763.33   $763.30   $763.40