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 $223.77   9.507%   $245.0438   $245.04   $245.05   $245.00  
  Purchase #2 $163.59   8.186%   $176.9815   $176.98   $177.00   $177.00  
  Purchase #3 $23.70   6.859%   $25.3256   $25.33   $25.35   $25.30  
  Purchase #4 $55.86   9.640%   $61.2449   $61.24   $61.25   $61.20  
  Purchase #5 $93.73   8.666%   $101.8526   $101.85   $101.85   $101.90  
  Purchase #6 $160.37   7.183%   $171.8894   $171.89   $171.90   $171.90  
  Purchase #7 $43.47   12.427%   $48.872   $48.87   $48.85   $48.90  
  7 purchase totals = $764.49       $831.2098   $831.20   $831.25   $831.20