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 $245.61   7.199%   $263.2915   $263.29   $263.30   $263.30  
  Purchase #2 $31.64   10.195%   $34.8657   $34.87   $34.85   $34.90  
  Purchase #3 $38.86   9.709%   $42.6329   $42.63   $42.65   $42.60  
  Purchase #4 $200.37   3.131%   $206.6436   $206.64   $206.65   $206.60  
  Purchase #5 $231.35   7.556%   $248.8308   $248.83   $248.85   $248.80  
  Purchase #6 $119.70   4.634%   $125.2469   $125.25   $125.25   $125.20  
  Purchase #7 $6.83   9.158%   $7.4555   $7.46   $7.45   $7.50  
  7 purchase totals = $874.36       $928.9669   $928.97   $929.00   $928.90