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	$23.90	6.186%	$25.3785	$25.38	$25.40	$25.40
Purchase #2	$115.55	7.354%	$124.0475	$124.05	$124.05	$124.00
Purchase #3	$43.50	12.468%	$48.9236	$48.92	$48.90	$48.90
Purchase #4	$171.96	4.387%	$179.5039	$179.50	$179.50	$179.50
Purchase #5	$153.66	12.351%	$172.6385	$172.64	$172.65	$172.60
Purchase #6	$25.73	9.276%	$28.1167	$28.12	$28.10	$28.10
Purchase #7	$96.34	4.550%	$100.7235	$100.72	$100.70	$100.70
7 purchase totals =	$630.64		$679.3322	$679.33	$679.30	$679.20