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	$64.95	12.266%	$72.9168	$72.92	$72.90	$72.90
Purchase #2	$241.67	13.862%	$275.1703	$275.17	$275.15	$275.20
Purchase #3	$228.93	5.848%	$242.3178	$242.32	$242.30	$242.30
Purchase #4	$148.39	4.657%	$155.3005	$155.30	$155.30	$155.30
Purchase #5	$245.28	5.717%	$259.3027	$259.30	$259.30	$259.30
Purchase #6	$198.39	12.811%	$223.8057	$223.81	$223.80	$223.80
Purchase #7	$159.50	12.362%	$179.2174	$179.22	$179.20	$179.20
7 purchase totals =	$1,287.11		$1,408.0312	$1,408.04	$1,407.95	$1,408.00