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	$21.45	6.232%	$22.7868	$22.79	$22.80	$22.80
Purchase #2	$152.59	8.398%	$165.4045	$165.40	$165.40	$165.40
Purchase #3	$168.48	11.819%	$188.3927	$188.39	$188.40	$188.40
Purchase #4	$145.54	9.469%	$159.3212	$159.32	$159.30	$159.30
Purchase #5	$99.92	10.268%	$110.1798	$110.18	$110.20	$110.20
Purchase #6	$241.59	13.639%	$274.5405	$274.54	$274.55	$274.50
Purchase #7	$63.39	13.414%	$71.8931	$71.89	$71.90	$71.90
7 purchase totals =	$892.96		$992.5186	$992.51	$992.55	$992.50