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	$33.52	12.294%	$37.6409	$37.64	$37.65	$37.60
Purchase #2	$88.57	11.816%	$99.0354	$99.04	$99.05	$99.00
Purchase #3	$46.87	8.502%	$50.8549	$50.85	$50.85	$50.90
Purchase #4	$138.65	4.564%	$144.978	$144.98	$145.00	$145.00
Purchase #5	$28.75	12.629%	$32.3808	$32.38	$32.40	$32.40
Purchase #6	$10.44	13.368%	$11.8356	$11.84	$11.85	$11.80
Purchase #7	$69.64	11.867%	$77.9042	$77.90	$77.90	$77.90
7 purchase totals =	$416.44		$454.6298	$454.63	$454.70	$454.60