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	$223.59	13.408%	$253.5689	$253.57	$253.55	$253.60
Purchase #2	$46.65	8.699%	$50.7081	$50.71	$50.70	$50.70
Purchase #3	$66.37	13.422%	$75.2782	$75.28	$75.30	$75.30
Purchase #4	$243.34	10.765%	$269.5356	$269.54	$269.55	$269.50
Purchase #5	$125.66	8.215%	$135.983	$135.98	$136.00	$136.00
Purchase #6	$89.33	12.451%	$100.4525	$100.45	$100.45	$100.50
Purchase #7	$109.35	7.113%	$117.1281	$117.13	$117.15	$117.10
7 purchase totals =	$904.29		$1,002.6544	$1,002.66	$1,002.70	$1,002.70