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	$139.60	10.480%	$154.2301	$154.23	$154.25	$154.20
Purchase #2	$17.80	6.239%	$18.9105	$18.91	$18.90	$18.90
Purchase #3	$235.92	6.290%	$250.7594	$250.76	$250.75	$250.80
Purchase #4	$122.74	3.751%	$127.344	$127.34	$127.35	$127.30
Purchase #5	$56.67	5.651%	$59.8724	$59.87	$59.85	$59.90
Purchase #6	$203.69	10.865%	$225.8209	$225.82	$225.80	$225.80
Purchase #7	$55.63	6.750%	$59.385	$59.39	$59.40	$59.40
7 purchase totals =	$832.05		$896.3223	$896.32	$896.30	$896.30