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 $246.50   8.705%   $267.9578   $267.96   $267.95   $268.00  
  Purchase #2 $85.96   5.204%   $90.4334   $90.43   $90.45   $90.40  
  Purchase #3 $171.68   12.105%   $192.4619   $192.46   $192.45   $192.50  
  Purchase #4 $93.67   9.566%   $102.6305   $102.63   $102.65   $102.60  
  Purchase #5 $116.35   5.566%   $122.826   $122.83   $122.85   $122.80  
  Purchase #6 $63.63   7.603%   $68.4678   $68.47   $68.45   $68.50  
  Purchase #7 $83.88   9.777%   $92.0809   $92.08   $92.10   $92.10  
  7 purchase totals = $861.67       $936.8583   $936.86   $936.90   $936.90