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	$40.34	11.309%	$44.9021	$44.90	$44.90	$44.90
Purchase #2	$120.47	11.624%	$134.4734	$134.47	$134.45	$134.50
Purchase #3	$129.40	11.669%	$144.4997	$144.50	$144.50	$144.50
Purchase #4	$45.66	11.505%	$50.9132	$50.91	$50.90	$50.90
Purchase #5	$144.56	5.796%	$152.9387	$152.94	$152.95	$152.90
Purchase #6	$51.67	4.433%	$53.9605	$53.96	$53.95	$54.00
Purchase #7	$55.76	8.775%	$60.6529	$60.65	$60.65	$60.70
7 purchase totals =	$587.86		$642.3405	$642.33	$642.30	$642.40