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 $112.51   12.218%   $126.2565   $126.26   $126.25   $126.30  
  Purchase #2 $85.41   13.137%   $96.6303   $96.63   $96.65   $96.60  
  Purchase #3 $209.25   11.602%   $233.5272   $233.53   $233.55   $233.50  
  Purchase #4 $240.31   13.481%   $272.7062   $272.71   $272.70   $272.70  
  Purchase #5 $89.99   13.336%   $101.9911   $101.99   $102.00   $102.00  
  Purchase #6 $174.30   6.614%   $185.8282   $185.83   $185.85   $185.80  
  Purchase #7 $25.61   13.347%   $29.0282   $29.03   $29.05   $29.00  
  7 purchase totals = $937.38       $1,045.9677   $1,045.98   $1,046.05   $1,045.90