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	$28.73	12.820%	$32.4132	$32.41	$32.40	$32.40
Purchase #2	$221.68	10.778%	$245.5727	$245.57	$245.55	$245.60
Purchase #3	$6.98	8.608%	$7.5808	$7.58	$7.60	$7.60
Purchase #4	$82.62	9.224%	$90.2409	$90.24	$90.25	$90.20
Purchase #5	$79.55	13.687%	$90.438	$90.44	$90.45	$90.40
Purchase #6	$111.43	13.428%	$126.3928	$126.39	$126.40	$126.40
Purchase #7	$157.73	12.584%	$177.5787	$177.58	$177.60	$177.60
7 purchase totals =	$688.72		$770.2171	$770.21	$770.25	$770.20