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	$159.33	6.386%	$169.5048	$169.50	$169.50	$169.50
Purchase #2	$137.32	3.776%	$142.5052	$142.51	$142.50	$142.50
Purchase #3	$22.42	11.171%	$24.9245	$24.92	$24.90	$24.90
Purchase #4	$146.91	9.169%	$160.3802	$160.38	$160.40	$160.40
Purchase #5	$169.83	12.482%	$191.0282	$191.03	$191.05	$191.00
Purchase #6	$42.45	7.480%	$45.6253	$45.63	$45.65	$45.60
Purchase #7	$28.70	4.146%	$29.8899	$29.89	$29.90	$29.90
7 purchase totals =	$706.96		$763.8581	$763.86	$763.90	$763.80