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	$18.68	8.487%	$20.2654	$20.27	$20.25	$20.30
Purchase #2	$236.82	4.547%	$247.5882	$247.59	$247.60	$247.60
Purchase #3	$241.44	10.290%	$266.2842	$266.28	$266.30	$266.30
Purchase #4	$174.25	8.272%	$188.664	$188.66	$188.65	$188.70
Purchase #5	$120.91	13.112%	$136.7637	$136.76	$136.75	$136.80
Purchase #6	$72.63	13.657%	$82.5491	$82.55	$82.55	$82.50
Purchase #7	$66.83	11.310%	$74.3885	$74.39	$74.40	$74.40
7 purchase totals =	$931.56		$1,016.5031	$1,016.50	$1,016.50	$1,016.60