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 $92.77   6.271%   $98.5876   $98.59   $98.60   $98.60  
  Purchase #2 $220.36   6.410%   $234.4851   $234.49   $234.50   $234.50  
  Purchase #3 $68.43   6.692%   $73.0093   $73.01   $73.00   $73.00  
  Purchase #4 $76.80   7.287%   $82.3964   $82.40   $82.40   $82.40  
  Purchase #5 $221.61   11.127%   $246.2685   $246.27   $246.25   $246.30  
  Purchase #6 $183.74   8.160%   $198.7332   $198.73   $198.75   $198.70  
  Purchase #7 $26.35   5.741%   $27.8628   $27.86   $27.85   $27.90  
  7 purchase totals = $890.06       $961.3429   $961.35   $961.35   $961.40