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	$100.61	8.562%	$109.2242	$109.22	$109.20	$109.20
Purchase #2	$233.80	5.110%	$245.7472	$245.75	$245.75	$245.70
Purchase #3	$71.74	11.588%	$80.0532	$80.05	$80.05	$80.10
Purchase #4	$139.67	4.108%	$145.4076	$145.41	$145.40	$145.40
Purchase #5	$143.33	6.111%	$152.0889	$152.09	$152.10	$152.10
Purchase #6	$181.32	12.828%	$204.5797	$204.58	$204.60	$204.60
Purchase #7	$231.32	4.810%	$242.4465	$242.45	$242.45	$242.40
7 purchase totals =	$1,101.79		$1,179.5473	$1,179.55	$1,179.55	$1,179.50