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	$172.56	3.221%	$178.1182	$178.12	$178.10	$178.10
Purchase #2	$86.70	3.684%	$89.894	$89.89	$89.90	$89.90
Purchase #3	$117.64	13.443%	$133.4543	$133.45	$133.45	$133.50
Purchase #4	$103.88	11.756%	$116.0921	$116.09	$116.10	$116.10
Purchase #5	$66.91	9.733%	$73.4224	$73.42	$73.40	$73.40
Purchase #6	$244.50	12.837%	$275.8865	$275.89	$275.90	$275.90
Purchase #7	$211.66	11.344%	$235.6707	$235.67	$235.65	$235.70
7 purchase totals =	$1,003.85		$1,102.5382	$1,102.53	$1,102.50	$1,102.60