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 $65.45   12.667%   $73.7406   $73.74   $73.75   $73.70  
  Purchase #2 $183.80   10.546%   $203.1835   $203.18   $203.20   $203.20  
  Purchase #3 $65.57   7.821%   $70.6982   $70.70   $70.70   $70.70  
  Purchase #4 $24.78   11.665%   $27.6706   $27.67   $27.65   $27.70  
  Purchase #5 $188.54   10.366%   $208.0841   $208.08   $208.10   $208.10  
  Purchase #6 $240.89   5.854%   $254.9917   $254.99   $255.00   $255.00  
  Purchase #7 $18.73   3.299%   $19.3479   $19.35   $19.35   $19.30  
  7 purchase totals = $787.76       $857.7166   $857.71   $857.75   $857.70