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	$42.72	11.256%	$47.5286	$47.53	$47.55	$47.50
Purchase #2	$67.98	6.146%	$72.1581	$72.16	$72.15	$72.20
Purchase #3	$243.45	13.643%	$276.6639	$276.66	$276.65	$276.70
Purchase #4	$124.44	11.760%	$139.0741	$139.07	$139.05	$139.10
Purchase #5	$241.40	11.632%	$269.4796	$269.48	$269.50	$269.50
Purchase #6	$91.27	4.368%	$95.2567	$95.26	$95.25	$95.30
Purchase #7	$49.34	12.532%	$55.5233	$55.52	$55.50	$55.50
7 purchase totals =	$860.60		$955.6843	$955.68	$955.65	$955.80