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	$247.73	4.403%	$258.6376	$258.64	$258.65	$258.60
Purchase #2	$60.74	10.836%	$67.3218	$67.32	$67.30	$67.30
Purchase #3	$97.70	9.638%	$107.1163	$107.12	$107.10	$107.10
Purchase #4	$228.61	6.352%	$243.1313	$243.13	$243.15	$243.10
Purchase #5	$20.59	3.851%	$21.3829	$21.38	$21.40	$21.40
Purchase #6	$30.89	11.244%	$34.3633	$34.36	$34.35	$34.40
Purchase #7	$59.38	3.572%	$61.5011	$61.50	$61.50	$61.50
7 purchase totals =	$745.64		$793.4543	$793.45	$793.45	$793.40