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 $212.84   6.187%   $226.0084   $226.01   $226.00   $226.00  
  Purchase #2 $250.63   9.830%   $275.2669   $275.27   $275.25   $275.30  
  Purchase #3 $159.64   3.766%   $165.652   $165.65   $165.65   $165.70  
  Purchase #4 $56.99   10.438%   $62.9386   $62.94   $62.95   $62.90  
  Purchase #5 $231.79   5.773%   $245.1712   $245.17   $245.15   $245.20  
  Purchase #6 $190.67   8.692%   $207.243   $207.24   $207.25   $207.20  
  Purchase #7 $215.66   7.689%   $232.2421   $232.24   $232.25   $232.20  
  7 purchase totals = $1,318.22       $1,414.5222   $1,414.52   $1,414.50   $1,414.50