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	$33.27	12.700%	$37.4953	$37.50	$37.50	$37.50
Purchase #2	$245.51	12.175%	$275.4008	$275.40	$275.40	$275.40
Purchase #3	$77.33	11.613%	$86.3103	$86.31	$86.30	$86.30
Purchase #4	$138.83	11.102%	$154.2429	$154.24	$154.25	$154.20
Purchase #5	$203.79	13.421%	$231.1407	$231.14	$231.15	$231.10
Purchase #6	$139.31	5.820%	$147.4178	$147.42	$147.40	$147.40
Purchase #7	$231.43	3.154%	$238.7293	$238.73	$238.75	$238.70
7 purchase totals =	$1,069.47		$1,170.7371	$1,170.74	$1,170.75	$1,170.60