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 $56.82   8.647%   $61.7332   $61.73   $61.75   $61.70  
  Purchase #2 $96.78   11.352%   $107.7665   $107.77   $107.75   $107.80  
  Purchase #3 $76.65   3.337%   $79.2078   $79.21   $79.20   $79.20  
  Purchase #4 $207.46   4.873%   $217.5695   $217.57   $217.55   $217.60  
  Purchase #5 $124.48   9.272%   $136.0218   $136.02   $136.00   $136.00  
  Purchase #6 $127.41   9.302%   $139.2617   $139.26   $139.25   $139.30  
  Purchase #7 $54.95   7.191%   $58.9015   $58.90   $58.90   $58.90  
  7 purchase totals = $744.55       $800.4620   $800.46   $800.40   $800.50