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 $176.41   10.133%   $194.2856   $194.29   $194.30   $194.30  
  Purchase #2 $237.85   8.471%   $257.9983   $258.00   $258.00   $258.00  
  Purchase #3 $35.96   10.371%   $39.6894   $39.69   $39.70   $39.70  
  Purchase #4 $40.89   6.433%   $43.5205   $43.52   $43.50   $43.50  
  Purchase #5 $206.72   4.358%   $215.7289   $215.73   $215.75   $215.70  
  Purchase #6 $199.35   12.602%   $224.4721   $224.47   $224.45   $224.50  
  Purchase #7 $247.35   11.553%   $275.9263   $275.93   $275.95   $275.90  
  7 purchase totals = $1,144.53       $1,251.6211   $1,251.63   $1,251.65   $1,251.60