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	$181.48	13.167%	$205.3755	$205.38	$205.40	$205.40
Purchase #2	$139.76	8.496%	$151.634	$151.63	$151.65	$151.60
Purchase #3	$43.39	5.381%	$45.7248	$45.72	$45.70	$45.70
Purchase #4	$245.53	13.700%	$279.1676	$279.17	$279.15	$279.20
Purchase #5	$235.94	7.816%	$254.3811	$254.38	$254.40	$254.40
Purchase #6	$188.52	6.817%	$201.3714	$201.37	$201.35	$201.40
Purchase #7	$80.99	5.422%	$85.3813	$85.38	$85.40	$85.40
7 purchase totals =	$1,115.61		$1,223.0357	$1,223.03	$1,223.05	$1,223.10