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	$150.92	13.392%	$171.1312	$171.13	$171.15	$171.10
Purchase #2	$82.91	10.259%	$91.4157	$91.42	$91.40	$91.40
Purchase #3	$87.60	8.298%	$94.869	$94.87	$94.85	$94.90
Purchase #4	$175.62	11.340%	$195.5353	$195.54	$195.55	$195.50
Purchase #5	$247.80	10.702%	$274.3196	$274.32	$274.30	$274.30
Purchase #6	$244.75	4.402%	$255.5239	$255.52	$255.50	$255.50
Purchase #7	$151.71	5.474%	$160.0146	$160.01	$160.00	$160.00
7 purchase totals =	$1,141.31		$1,242.8093	$1,242.81	$1,242.75	$1,242.70