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	$17.56	3.725%	$18.2141	$18.21	$18.20	$18.20
Purchase #2	$99.60	7.338%	$106.9086	$106.91	$106.90	$106.90
Purchase #3	$206.96	9.194%	$225.9879	$225.99	$226.00	$226.00
Purchase #4	$128.31	10.112%	$141.2847	$141.28	$141.30	$141.30
Purchase #5	$219.96	9.303%	$240.4229	$240.42	$240.40	$240.40
Purchase #6	$100.88	8.760%	$109.7171	$109.72	$109.70	$109.70
Purchase #7	$105.38	5.695%	$111.3814	$111.38	$111.40	$111.40
7 purchase totals =	$878.65		$953.9167	$953.91	$953.90	$953.90