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	$13.78	10.593%	$15.2397	$15.24	$15.25	$15.20
Purchase #2	$111.56	4.174%	$116.2165	$116.22	$116.20	$116.20
Purchase #3	$68.48	6.218%	$72.7381	$72.74	$72.75	$72.70
Purchase #4	$140.77	7.349%	$151.1152	$151.12	$151.10	$151.10
Purchase #5	$31.25	10.622%	$34.5694	$34.57	$34.55	$34.60
Purchase #6	$145.66	4.674%	$152.4681	$152.47	$152.45	$152.50
Purchase #7	$24.47	10.107%	$26.9432	$26.94	$26.95	$26.90
7 purchase totals =	$535.97		$569.2902	$569.30	$569.25	$569.20