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 $243.78   9.787%   $267.6387   $267.64   $267.65   $267.60  
  Purchase #2 $126.78   11.711%   $141.6272   $141.63   $141.65   $141.60  
  Purchase #3 $162.57   7.653%   $175.0115   $175.01   $175.00   $175.00  
  Purchase #4 $142.28   4.120%   $148.1419   $148.14   $148.15   $148.10  
  Purchase #5 $98.91   7.588%   $106.4153   $106.42   $106.40   $106.40  
  Purchase #6 $51.67   6.265%   $54.9071   $54.91   $54.90   $54.90  
  Purchase #7 $37.69   4.370%   $39.3371   $39.34   $39.35   $39.30  
  7 purchase totals = $863.68       $933.0788   $933.09   $933.10   $932.90