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	$147.89	11.650%	$165.1192	$165.12	$165.10	$165.10
Purchase #2	$139.65	5.415%	$147.212	$147.21	$147.20	$147.20
Purchase #3	$178.62	9.846%	$196.2069	$196.21	$196.20	$196.20
Purchase #4	$184.92	8.366%	$200.3904	$200.39	$200.40	$200.40
Purchase #5	$46.43	9.468%	$50.826	$50.83	$50.85	$50.80
Purchase #6	$37.44	13.795%	$42.6048	$42.60	$42.60	$42.60
Purchase #7	$50.28	6.614%	$53.6055	$53.61	$53.60	$53.60
7 purchase totals =	$785.23		$855.9648	$855.97	$855.95	$855.90