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	$244.28	8.407%	$264.8166	$264.82	$264.80	$264.80
Purchase #2	$156.90	7.631%	$168.873	$168.87	$168.85	$168.90
Purchase #3	$56.86	13.623%	$64.606	$64.61	$64.60	$64.60
Purchase #4	$159.87	3.251%	$165.0674	$165.07	$165.05	$165.10
Purchase #5	$13.92	11.659%	$15.5429	$15.54	$15.55	$15.50
Purchase #6	$108.55	9.257%	$118.5985	$118.60	$118.60	$118.60
Purchase #7	$37.48	10.785%	$41.5222	$41.52	$41.50	$41.50
7 purchase totals =	$777.86		$839.0266	$839.03	$838.95	$839.00