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	$134.70	13.663%	$153.1041	$153.10	$153.10	$153.10
Purchase #2	$15.57	3.654%	$16.1389	$16.14	$16.15	$16.10
Purchase #3	$81.40	10.847%	$90.2295	$90.23	$90.25	$90.20
Purchase #4	$31.59	9.557%	$34.6091	$34.61	$34.60	$34.60
Purchase #5	$232.37	3.743%	$241.0676	$241.07	$241.05	$241.10
Purchase #6	$99.42	9.814%	$109.1771	$109.18	$109.20	$109.20
Purchase #7	$15.38	4.847%	$16.1255	$16.13	$16.15	$16.10
7 purchase totals =	$610.43		$660.4518	$660.46	$660.50	$660.40