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	$248.39	13.685%	$282.3822	$282.38	$282.40	$282.40
Purchase #2	$124.25	5.461%	$131.0353	$131.04	$131.05	$131.00
Purchase #3	$167.44	13.366%	$189.82	$189.82	$189.80	$189.80
Purchase #4	$52.63	12.690%	$59.3087	$59.31	$59.30	$59.30
Purchase #5	$175.82	11.266%	$195.6279	$195.63	$195.65	$195.60
Purchase #6	$231.61	12.617%	$260.8322	$260.83	$260.85	$260.80
Purchase #7	$55.84	8.208%	$60.4233	$60.42	$60.40	$60.40
7 purchase totals =	$1,055.98		$1,179.4296	$1,179.43	$1,179.45	$1,179.30