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	$168.96	6.839%	$180.5152	$180.52	$180.50	$180.50
Purchase #2	$49.67	8.265%	$53.7752	$53.78	$53.80	$53.80
Purchase #3	$129.92	13.512%	$147.4748	$147.47	$147.45	$147.50
Purchase #4	$195.35	10.796%	$216.44	$216.44	$216.45	$216.40
Purchase #5	$99.41	7.381%	$106.7475	$106.75	$106.75	$106.70
Purchase #6	$151.61	9.353%	$165.7901	$165.79	$165.80	$165.80
Purchase #7	$250.85	7.167%	$268.8284	$268.83	$268.85	$268.80
7 purchase totals =	$1,045.77		$1,139.5712	$1,139.58	$1,139.60	$1,139.50