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	$244.64	12.112%	$274.2708	$274.27	$274.25	$274.30
Purchase #2	$240.91	11.773%	$269.2723	$269.27	$269.25	$269.30
Purchase #3	$174.94	6.244%	$185.8633	$185.86	$185.85	$185.90
Purchase #4	$113.72	6.378%	$120.9731	$120.97	$120.95	$121.00
Purchase #5	$67.94	5.368%	$71.587	$71.59	$71.60	$71.60
Purchase #6	$225.45	13.495%	$255.8745	$255.87	$255.85	$255.90
Purchase #7	$185.56	10.109%	$204.3183	$204.32	$204.30	$204.30
7 purchase totals =	$1,253.16		$1,382.1593	$1,382.15	$1,382.05	$1,382.30