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	$44.33	13.109%	$50.1412	$50.14	$50.15	$50.10
Purchase #2	$66.80	6.662%	$71.2502	$71.25	$71.25	$71.30
Purchase #3	$173.50	3.186%	$179.0277	$179.03	$179.05	$179.00
Purchase #4	$224.73	4.768%	$235.4451	$235.45	$235.45	$235.40
Purchase #5	$96.36	4.585%	$100.7781	$100.78	$100.80	$100.80
Purchase #6	$66.75	7.342%	$71.6508	$71.65	$71.65	$71.70
Purchase #7	$137.90	3.821%	$143.1692	$143.17	$143.15	$143.20
7 purchase totals =	$810.37		$851.4623	$851.47	$851.50	$851.50