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	$151.87	5.346%	$159.989	$159.99	$160.00	$160.00
Purchase #2	$245.75	11.840%	$274.8468	$274.85	$274.85	$274.80
Purchase #3	$78.56	8.504%	$85.2407	$85.24	$85.25	$85.20
Purchase #4	$137.97	13.504%	$156.6015	$156.60	$156.60	$156.60
Purchase #5	$104.82	6.759%	$111.9048	$111.90	$111.90	$111.90
Purchase #6	$50.84	8.489%	$55.1558	$55.16	$55.15	$55.20
Purchase #7	$135.83	12.631%	$152.9867	$152.99	$153.00	$153.00
7 purchase totals =	$905.64		$996.7253	$996.73	$996.75	$996.70