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	$87.89	13.236%	$99.5231	$99.52	$99.50	$99.50
Purchase #2	$91.29	13.439%	$103.5585	$103.56	$103.55	$103.60
Purchase #3	$103.81	10.204%	$114.4028	$114.40	$114.40	$114.40
Purchase #4	$160.62	8.849%	$174.8333	$174.83	$174.85	$174.80
Purchase #5	$94.84	4.138%	$98.7645	$98.76	$98.75	$98.80
Purchase #6	$123.49	4.601%	$129.1718	$129.17	$129.15	$129.20
Purchase #7	$200.72	4.265%	$209.2807	$209.28	$209.30	$209.30
7 purchase totals =	$862.66		$929.5347	$929.52	$929.50	$929.60