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	$74.58	4.820%	$78.1748	$78.17	$78.15	$78.20
Purchase #2	$102.69	12.608%	$115.6372	$115.64	$115.65	$115.60
Purchase #3	$28.94	8.812%	$31.4902	$31.49	$31.50	$31.50
Purchase #4	$225.62	13.212%	$255.4289	$255.43	$255.45	$255.40
Purchase #5	$136.48	10.637%	$150.9974	$151.00	$151.00	$151.00
Purchase #6	$161.29	5.488%	$170.1416	$170.14	$170.15	$170.10
Purchase #7	$198.61	8.806%	$216.0996	$216.10	$216.10	$216.10
7 purchase totals =	$928.21		$1,017.9697	$1,017.97	$1,018.00	$1,017.90