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	$47.64	12.329%	$53.5135	$53.51	$53.50	$53.50
Purchase #2	$34.27	4.735%	$35.8927	$35.89	$35.90	$35.90
Purchase #3	$103.71	6.858%	$110.8224	$110.82	$110.80	$110.80
Purchase #4	$58.25	6.251%	$61.8912	$61.89	$61.90	$61.90
Purchase #5	$15.70	4.111%	$16.3454	$16.35	$16.35	$16.30
Purchase #6	$108.80	3.386%	$112.484	$112.48	$112.50	$112.50
Purchase #7	$227.59	6.350%	$242.042	$242.04	$242.05	$242.00
7 purchase totals =	$595.96		$632.9912	$632.98	$633.00	$632.90