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	$106.76	4.761%	$111.8428	$111.84	$111.85	$111.80
Purchase #2	$154.25	10.326%	$170.1779	$170.18	$170.20	$170.20
Purchase #3	$159.47	10.575%	$176.334	$176.33	$176.35	$176.30
Purchase #4	$50.96	12.580%	$57.3708	$57.37	$57.35	$57.40
Purchase #5	$107.86	13.465%	$122.3833	$122.38	$122.40	$122.40
Purchase #6	$86.28	3.377%	$89.1937	$89.19	$89.20	$89.20
Purchase #7	$39.35	10.612%	$43.5258	$43.53	$43.55	$43.50
7 purchase totals =	$704.93		$770.8283	$770.82	$770.90	$770.80