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	$44.51	11.784%	$49.7551	$49.76	$49.75	$49.80
Purchase #2	$59.52	13.791%	$67.7284	$67.73	$67.75	$67.70
Purchase #3	$10.33	5.188%	$10.8659	$10.87	$10.85	$10.90
Purchase #4	$115.45	3.129%	$119.0624	$119.06	$119.05	$119.10
Purchase #5	$177.76	12.390%	$199.7845	$199.78	$199.80	$199.80
Purchase #6	$113.99	12.571%	$128.3197	$128.32	$128.30	$128.30
Purchase #7	$171.76	13.468%	$194.8926	$194.89	$194.90	$194.90
7 purchase totals =	$693.32		$770.4086	$770.41	$770.40	$770.50