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	$247.91	13.196%	$280.6242	$280.62	$280.60	$280.60
Purchase #2	$121.67	7.303%	$130.5556	$130.56	$130.55	$130.60
Purchase #3	$135.89	11.576%	$151.6206	$151.62	$151.60	$151.60
Purchase #4	$141.33	8.384%	$153.1791	$153.18	$153.20	$153.20
Purchase #5	$196.40	4.472%	$205.183	$205.18	$205.20	$205.20
Purchase #6	$185.87	3.250%	$191.9108	$191.91	$191.90	$191.90
Purchase #7	$242.25	13.351%	$274.5928	$274.59	$274.60	$274.60
7 purchase totals =	$1,271.32		$1,387.6661	$1,387.66	$1,387.65	$1,387.70