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	$233.71	5.819%	$247.3096	$247.31	$247.30	$247.30
Purchase #2	$160.42	11.288%	$178.5282	$178.53	$178.55	$178.50
Purchase #3	$29.29	12.401%	$32.9223	$32.92	$32.90	$32.90
Purchase #4	$145.70	9.375%	$159.3594	$159.36	$159.35	$159.40
Purchase #5	$249.27	12.500%	$280.4288	$280.43	$280.45	$280.40
Purchase #6	$131.38	6.793%	$140.3046	$140.30	$140.30	$140.30
Purchase #7	$138.50	12.864%	$156.3166	$156.32	$156.30	$156.30
7 purchase totals =	$1,088.27		$1,195.1695	$1,195.17	$1,195.15	$1,195.10