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	$105.76	3.391%	$109.3463	$109.35	$109.35	$109.30
Purchase #2	$31.86	7.691%	$34.3104	$34.31	$34.30	$34.30
Purchase #3	$209.82	3.267%	$216.6748	$216.67	$216.65	$216.70
Purchase #4	$48.50	12.759%	$54.6881	$54.69	$54.70	$54.70
Purchase #5	$118.47	7.481%	$127.3327	$127.33	$127.35	$127.30
Purchase #6	$107.63	5.145%	$113.1676	$113.17	$113.15	$113.20
Purchase #7	$61.42	6.466%	$65.3914	$65.39	$65.40	$65.40
7 purchase totals =	$683.46		$720.9113	$720.91	$720.90	$720.90