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	$242.50	3.103%	$250.0248	$250.02	$250.00	$250.00
Purchase #2	$53.82	5.873%	$56.9808	$56.98	$57.00	$57.00
Purchase #3	$55.48	10.642%	$61.3842	$61.38	$61.40	$61.40
Purchase #4	$59.28	13.705%	$67.4043	$67.40	$67.40	$67.40
Purchase #5	$116.41	11.852%	$130.2069	$130.21	$130.20	$130.20
Purchase #6	$145.65	6.670%	$155.3649	$155.36	$155.35	$155.40
Purchase #7	$155.54	4.248%	$162.1473	$162.15	$162.15	$162.10
7 purchase totals =	$828.68		$883.5132	$883.50	$883.50	$883.50