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	$99.30	5.746%	$105.0058	$105.01	$105.00	$105.00
Purchase #2	$89.51	6.739%	$95.5421	$95.54	$95.55	$95.50
Purchase #3	$157.33	8.143%	$170.1414	$170.14	$170.15	$170.10
Purchase #4	$31.61	7.466%	$33.97	$33.97	$33.95	$34.00
Purchase #5	$212.56	12.296%	$238.6964	$238.70	$238.70	$238.70
Purchase #6	$234.91	3.175%	$242.3684	$242.37	$242.35	$242.40
Purchase #7	$20.69	4.857%	$21.6949	$21.69	$21.70	$21.70
7 purchase totals =	$845.91		$907.4190	$907.42	$907.40	$907.40