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	$32.98	12.573%	$37.1266	$37.13	$37.15	$37.10
Purchase #2	$154.55	8.557%	$167.7748	$167.77	$167.75	$167.80
Purchase #3	$126.90	12.291%	$142.4973	$142.50	$142.50	$142.50
Purchase #4	$242.87	8.302%	$263.0331	$263.03	$263.05	$263.00
Purchase #5	$229.60	13.365%	$260.286	$260.29	$260.30	$260.30
Purchase #6	$218.34	11.864%	$244.2439	$244.24	$244.25	$244.20
Purchase #7	$134.89	11.651%	$150.606	$150.61	$150.60	$150.60
7 purchase totals =	$1,140.13		$1,265.5677	$1,265.57	$1,265.60	$1,265.50