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	$244.51	7.718%	$263.3813	$263.38	$263.40	$263.40
Purchase #2	$144.85	3.587%	$150.0458	$150.05	$150.05	$150.00
Purchase #3	$175.67	5.488%	$185.3108	$185.31	$185.30	$185.30
Purchase #4	$86.45	10.599%	$95.6128	$95.61	$95.60	$95.60
Purchase #5	$234.61	13.306%	$265.8272	$265.83	$265.85	$265.80
Purchase #6	$229.98	8.707%	$250.0044	$250.00	$250.00	$250.00
Purchase #7	$144.57	10.482%	$159.7238	$159.72	$159.70	$159.70
7 purchase totals =	$1,260.64		$1,369.9061	$1,369.90	$1,369.90	$1,369.80