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	$106.90	4.253%	$111.4465	$111.45	$111.45	$111.40
Purchase #2	$246.89	9.691%	$270.8161	$270.82	$270.80	$270.80
Purchase #3	$11.32	8.857%	$12.3226	$12.32	$12.30	$12.30
Purchase #4	$208.52	12.153%	$233.8614	$233.86	$233.85	$233.90
Purchase #5	$21.85	13.453%	$24.7895	$24.79	$24.80	$24.80
Purchase #6	$30.71	11.804%	$34.335	$34.34	$34.35	$34.30
Purchase #7	$142.56	3.245%	$147.1861	$147.19	$147.20	$147.20
7 purchase totals =	$768.75		$834.7572	$834.77	$834.75	$834.70