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	$44.62	13.713%	$50.7387	$50.74	$50.75	$50.70
Purchase #2	$78.82	13.397%	$89.3795	$89.38	$89.40	$89.40
Purchase #3	$106.47	5.622%	$112.4557	$112.46	$112.45	$112.50
Purchase #4	$69.41	6.375%	$73.8349	$73.83	$73.85	$73.80
Purchase #5	$227.74	9.276%	$248.8652	$248.87	$248.85	$248.90
Purchase #6	$8.33	6.710%	$8.8889	$8.89	$8.90	$8.90
Purchase #7	$28.91	9.354%	$31.6142	$31.61	$31.60	$31.60
7 purchase totals =	$564.30		$615.7771	$615.78	$615.80	$615.80