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 $196.53   13.278%   $222.6253   $222.63   $222.65   $222.60  
  Purchase #2 $160.86   8.107%   $173.9009   $173.90   $173.90   $173.90  
  Purchase #3 $238.52   7.210%   $255.7173   $255.72   $255.70   $255.70  
  Purchase #4 $61.44   5.203%   $64.6367   $64.64   $64.65   $64.60  
  Purchase #5 $186.96   10.201%   $206.0318   $206.03   $206.05   $206.00  
  Purchase #6 $227.83   3.522%   $235.8542   $235.85   $235.85   $235.90  
  Purchase #7 $182.46   9.589%   $199.9561   $199.96   $199.95   $200.00  
  7 purchase totals = $1,254.60       $1,358.7223   $1,358.73   $1,358.75   $1,358.70