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	$227.37	12.543%	$255.889	$255.89	$255.90	$255.90
Purchase #2	$131.74	4.625%	$137.833	$137.83	$137.85	$137.80
Purchase #3	$92.28	8.489%	$100.1136	$100.11	$100.10	$100.10
Purchase #4	$65.72	11.834%	$73.4973	$73.50	$73.50	$73.50
Purchase #5	$100.70	11.528%	$112.3087	$112.31	$112.30	$112.30
Purchase #6	$247.38	3.196%	$255.2863	$255.29	$255.30	$255.30
Purchase #7	$69.53	11.519%	$77.5392	$77.54	$77.55	$77.50
7 purchase totals =	$934.72		$1,012.4671	$1,012.47	$1,012.50	$1,012.40