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 $236.64   11.284%   $263.3425   $263.34   $263.35   $263.30  
  Purchase #2 $111.32   12.264%   $124.9723   $124.97   $124.95   $125.00  
  Purchase #3 $114.86   3.428%   $118.7974   $118.80   $118.80   $118.80  
  Purchase #4 $8.85   13.125%   $10.0116   $10.01   $10.00   $10.00  
  Purchase #5 $127.64   9.281%   $139.4863   $139.49   $139.50   $139.50  
  Purchase #6 $110.46   8.535%   $119.8878   $119.89   $119.90   $119.90  
  Purchase #7 $112.99   7.389%   $121.3388   $121.34   $121.35   $121.30  
  7 purchase totals = $822.76       $897.8367   $897.84   $897.85   $897.80