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	$250.69	3.282%	$258.9176	$258.92	$258.90	$258.90
Purchase #2	$23.46	9.399%	$25.665	$25.67	$25.65	$25.70
Purchase #3	$10.51	12.442%	$11.8177	$11.82	$11.80	$11.80
Purchase #4	$74.78	4.535%	$78.1713	$78.17	$78.15	$78.20
Purchase #5	$54.55	8.740%	$59.3177	$59.32	$59.30	$59.30
Purchase #6	$148.67	13.513%	$168.7598	$168.76	$168.75	$168.80
Purchase #7	$130.62	5.342%	$137.5977	$137.60	$137.60	$137.60
7 purchase totals =	$693.28		$740.2468	$740.26	$740.15	$740.30