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 $98.59   4.495%   $103.0216   $103.02   $103.00   $103.00  
  Purchase #2 $206.82   3.792%   $214.6626   $214.66   $214.65   $214.70  
  Purchase #3 $24.66   11.289%   $27.4439   $27.44   $27.45   $27.40  
  Purchase #4 $189.45   7.396%   $203.4617   $203.46   $203.45   $203.50  
  Purchase #5 $69.89   7.395%   $75.0584   $75.06   $75.05   $75.10  
  Purchase #6 $131.28   13.838%   $149.4465   $149.45   $149.45   $149.40  
  Purchase #7 $137.51   10.469%   $151.9059   $151.91   $151.90   $151.90  
  7 purchase totals = $858.20       $925.0006   $925.00   $924.95   $925.00