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	$250.61	9.345%	$274.0295	$274.03	$274.05	$274.00
Purchase #2	$142.50	7.118%	$152.6432	$152.64	$152.65	$152.60
Purchase #3	$194.87	10.327%	$214.9942	$214.99	$215.00	$215.00
Purchase #4	$155.93	10.235%	$171.8894	$171.89	$171.90	$171.90
Purchase #5	$231.90	4.732%	$242.8735	$242.87	$242.85	$242.90
Purchase #6	$227.87	4.813%	$238.8374	$238.84	$238.85	$238.80
Purchase #7	$18.52	10.578%	$20.479	$20.48	$20.50	$20.50
7 purchase totals =	$1,222.20		$1,315.7462	$1,315.74	$1,315.80	$1,315.70