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	$88.87	8.210%	$96.1662	$96.17	$96.15	$96.20
Purchase #2	$233.61	3.129%	$240.9197	$240.92	$240.90	$240.90
Purchase #3	$141.25	7.716%	$152.1489	$152.15	$152.15	$152.10
Purchase #4	$66.99	7.737%	$72.173	$72.17	$72.15	$72.20
Purchase #5	$221.41	11.510%	$246.8943	$246.89	$246.90	$246.90
Purchase #6	$70.61	13.474%	$80.124	$80.12	$80.10	$80.10
Purchase #7	$24.87	12.589%	$28.0009	$28.00	$28.00	$28.00
7 purchase totals =	$847.61		$916.4270	$916.42	$916.35	$916.40