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 $198.81   12.650%   $223.9595   $223.96   $223.95   $224.00  
  Purchase #2 $149.38   8.200%   $161.6292   $161.63   $161.65   $161.60  
  Purchase #3 $13.34   8.860%   $14.5219   $14.52   $14.50   $14.50  
  Purchase #4 $95.85   6.511%   $102.0908   $102.09   $102.10   $102.10  
  Purchase #5 $118.52   11.369%   $131.9945   $131.99   $132.00   $132.00  
  Purchase #6 $51.83   11.551%   $57.8169   $57.82   $57.80   $57.80  
  Purchase #7 $208.32   12.742%   $234.8641   $234.86   $234.85   $234.90  
  7 purchase totals = $836.05       $926.8769   $926.87   $926.85   $926.90