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	$137.70	5.589%	$145.3961	$145.40	$145.40	$145.40
Purchase #2	$140.49	6.651%	$149.834	$149.83	$149.85	$149.80
Purchase #3	$179.42	9.588%	$196.6228	$196.62	$196.60	$196.60
Purchase #4	$165.40	13.334%	$187.4544	$187.45	$187.45	$187.50
Purchase #5	$109.83	9.227%	$119.964	$119.96	$119.95	$120.00
Purchase #6	$28.71	6.620%	$30.6106	$30.61	$30.60	$30.60
Purchase #7	$165.67	4.584%	$173.2643	$173.26	$173.25	$173.30
7 purchase totals =	$927.22		$1,003.1462	$1,003.13	$1,003.10	$1,003.20