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	$113.74	13.395%	$128.9755	$128.98	$129.00	$129.00
Purchase #2	$33.80	10.743%	$37.4311	$37.43	$37.45	$37.40
Purchase #3	$164.86	3.672%	$170.9137	$170.91	$170.90	$170.90
Purchase #4	$16.64	9.537%	$18.227	$18.23	$18.25	$18.20
Purchase #5	$204.49	7.398%	$219.6182	$219.62	$219.60	$219.60
Purchase #6	$49.80	7.690%	$53.6296	$53.63	$53.65	$53.60
Purchase #7	$99.34	6.206%	$105.505	$105.51	$105.50	$105.50
7 purchase totals =	$682.67		$734.3001	$734.31	$734.35	$734.20