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	$42.74	9.501%	$46.8007	$46.80	$46.80	$46.80
Purchase #2	$53.42	3.407%	$55.24	$55.24	$55.25	$55.20
Purchase #3	$133.54	4.380%	$139.3891	$139.39	$139.40	$139.40
Purchase #4	$147.48	11.840%	$164.9416	$164.94	$164.95	$164.90
Purchase #5	$92.37	7.248%	$99.065	$99.07	$99.05	$99.10
Purchase #6	$211.43	4.822%	$221.6252	$221.63	$221.65	$221.60
Purchase #7	$92.54	11.853%	$103.5088	$103.51	$103.50	$103.50
7 purchase totals =	$773.52		$830.5704	$830.58	$830.60	$830.50