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	$69.61	6.797%	$74.3414	$74.34	$74.35	$74.30
Purchase #2	$204.43	7.372%	$219.5006	$219.50	$219.50	$219.50
Purchase #3	$129.43	5.706%	$136.8153	$136.82	$136.80	$136.80
Purchase #4	$222.56	10.286%	$245.4525	$245.45	$245.45	$245.50
Purchase #5	$207.71	11.227%	$231.0296	$231.03	$231.05	$231.00
Purchase #6	$115.56	13.793%	$131.4992	$131.50	$131.50	$131.50
Purchase #7	$91.96	9.588%	$100.7771	$100.78	$100.80	$100.80
7 purchase totals =	$1,041.26		$1,139.4157	$1,139.42	$1,139.45	$1,139.40