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	$108.93	10.824%	$120.7206	$120.72	$120.70	$120.70
Purchase #2	$20.79	11.404%	$23.1609	$23.16	$23.15	$23.20
Purchase #3	$74.91	4.132%	$78.0053	$78.01	$78.00	$78.00
Purchase #4	$89.39	13.321%	$101.2976	$101.30	$101.30	$101.30
Purchase #5	$93.34	4.171%	$97.2332	$97.23	$97.25	$97.20
Purchase #6	$6.70	12.525%	$7.5392	$7.54	$7.55	$7.50
Purchase #7	$52.42	4.708%	$54.8879	$54.89	$54.90	$54.90
7 purchase totals =	$446.48		$482.8447	$482.85	$482.85	$482.80