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	$229.93	4.686%	$240.7045	$240.70	$240.70	$240.70
Purchase #2	$71.56	9.721%	$78.5163	$78.52	$78.50	$78.50
Purchase #3	$52.56	5.363%	$55.3788	$55.38	$55.40	$55.40
Purchase #4	$45.66	9.733%	$50.1041	$50.10	$50.10	$50.10
Purchase #5	$124.67	9.124%	$136.0449	$136.04	$136.05	$136.00
Purchase #6	$41.78	10.557%	$46.1907	$46.19	$46.20	$46.20
Purchase #7	$33.25	6.600%	$35.4445	$35.44	$35.45	$35.40
7 purchase totals =	$599.41		$642.3838	$642.37	$642.40	$642.30