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	$50.97	12.336%	$57.2577	$57.26	$57.25	$57.30
Purchase #2	$91.40	7.104%	$97.8931	$97.89	$97.90	$97.90
Purchase #3	$84.80	5.321%	$89.3122	$89.31	$89.30	$89.30
Purchase #4	$74.39	3.283%	$76.8322	$76.83	$76.85	$76.80
Purchase #5	$169.53	13.685%	$192.7302	$192.73	$192.75	$192.70
Purchase #6	$33.43	7.297%	$35.8694	$35.87	$35.85	$35.90
Purchase #7	$130.88	6.599%	$139.5168	$139.52	$139.50	$139.50
7 purchase totals =	$635.40		$689.4116	$689.41	$689.40	$689.40