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	$229.65	4.156%	$239.1943	$239.19	$239.20	$239.20
Purchase #2	$181.58	12.129%	$203.6038	$203.60	$203.60	$203.60
Purchase #3	$78.73	8.118%	$85.1213	$85.12	$85.10	$85.10
Purchase #4	$220.35	13.811%	$250.7825	$250.78	$250.80	$250.80
Purchase #5	$152.55	4.393%	$159.2515	$159.25	$159.25	$159.30
Purchase #6	$74.77	13.839%	$85.1174	$85.12	$85.10	$85.10
Purchase #7	$63.79	5.700%	$67.426	$67.43	$67.45	$67.40
7 purchase totals =	$1,001.42		$1,090.4968	$1,090.49	$1,090.50	$1,090.50