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 $227.31   11.306%   $253.0097   $253.01   $253.00   $253.00  
  Purchase #2 $205.85   8.108%   $222.5403   $222.54   $222.55   $222.50  
  Purchase #3 $217.25   3.292%   $224.4019   $224.40   $224.40   $224.40  
  Purchase #4 $223.81   3.704%   $232.0999   $232.10   $232.10   $232.10  
  Purchase #5 $136.92   9.746%   $150.2642   $150.26   $150.25   $150.30  
  Purchase #6 $222.60   10.406%   $245.7638   $245.76   $245.75   $245.80  
  Purchase #7 $157.65   5.256%   $165.9361   $165.94   $165.95   $165.90  
  7 purchase totals = $1,391.39       $1,494.0159   $1,494.01   $1,494.00   $1,494.00