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	$104.87	6.476%	$111.6614	$111.66	$111.65	$111.70
Purchase #2	$111.42	7.562%	$119.8456	$119.85	$119.85	$119.80
Purchase #3	$168.34	7.306%	$180.6389	$180.64	$180.65	$180.60
Purchase #4	$89.58	5.407%	$94.4236	$94.42	$94.40	$94.40
Purchase #5	$74.38	11.799%	$83.1561	$83.16	$83.15	$83.20
Purchase #6	$20.56	6.845%	$21.9673	$21.97	$21.95	$22.00
Purchase #7	$30.80	5.731%	$32.5651	$32.57	$32.55	$32.60
7 purchase totals =	$599.95		$644.2580	$644.27	$644.20	$644.30