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	$130.94	5.413%	$138.0278	$138.03	$138.05	$138.00
Purchase #2	$139.79	4.165%	$145.6123	$145.61	$145.60	$145.60
Purchase #3	$105.29	10.319%	$116.1549	$116.15	$116.15	$116.20
Purchase #4	$121.91	5.397%	$128.4895	$128.49	$128.50	$128.50
Purchase #5	$57.27	5.227%	$60.2635	$60.26	$60.25	$60.30
Purchase #6	$80.71	10.505%	$89.1886	$89.19	$89.20	$89.20
Purchase #7	$98.36	8.298%	$106.5219	$106.52	$106.50	$106.50
7 purchase totals =	$734.27		$784.2585	$784.25	$784.25	$784.30