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	$212.37	4.728%	$222.4109	$222.41	$222.40	$222.40
Purchase #2	$84.42	7.183%	$90.4839	$90.48	$90.50	$90.50
Purchase #3	$149.72	13.448%	$169.8543	$169.85	$169.85	$169.90
Purchase #4	$172.40	11.563%	$192.3346	$192.33	$192.35	$192.30
Purchase #5	$123.41	7.694%	$132.9052	$132.91	$132.90	$132.90
Purchase #6	$130.68	9.230%	$142.7418	$142.74	$142.75	$142.70
Purchase #7	$126.35	8.190%	$136.6981	$136.70	$136.70	$136.70
7 purchase totals =	$999.35		$1,087.4288	$1,087.42	$1,087.45	$1,087.40