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 $53.64   11.855%   $59.999   $60.00   $60.00   $60.00  
  Purchase #2 $79.31   6.859%   $84.7499   $84.75   $84.75   $84.70  
  Purchase #3 $62.71   13.836%   $71.3866   $71.39   $71.40   $71.40  
  Purchase #4 $202.54   5.127%   $212.9242   $212.92   $212.90   $212.90  
  Purchase #5 $161.86   9.686%   $177.5378   $177.54   $177.55   $177.50  
  Purchase #6 $140.68   4.107%   $146.4577   $146.46   $146.45   $146.50  
  Purchase #7 $183.63   12.678%   $206.9106   $206.91   $206.90   $206.90  
  7 purchase totals = $884.37       $959.9658   $959.97   $959.95   $959.90