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	$217.30	11.710%	$242.7458	$242.75	$242.75	$242.70
Purchase #2	$148.27	11.817%	$165.7911	$165.79	$165.80	$165.80
Purchase #3	$229.33	6.538%	$244.3236	$244.32	$244.30	$244.30
Purchase #4	$165.92	7.470%	$178.3142	$178.31	$178.30	$178.30
Purchase #5	$103.87	3.666%	$107.6779	$107.68	$107.70	$107.70
Purchase #6	$233.59	4.662%	$244.48	$244.48	$244.50	$244.50
Purchase #7	$66.55	8.811%	$72.4137	$72.41	$72.40	$72.40
7 purchase totals =	$1,164.83		$1,255.7463	$1,255.74	$1,255.75	$1,255.70