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	$192.35	7.557%	$206.8859	$206.89	$206.90	$206.90
Purchase #2	$84.49	10.718%	$93.5456	$93.55	$93.55	$93.50
Purchase #3	$29.92	13.490%	$33.9562	$33.96	$33.95	$34.00
Purchase #4	$116.26	10.389%	$128.3383	$128.34	$128.35	$128.30
Purchase #5	$34.68	4.750%	$36.3273	$36.33	$36.35	$36.30
Purchase #6	$81.30	10.340%	$89.7064	$89.71	$89.70	$89.70
Purchase #7	$103.51	7.611%	$111.3881	$111.39	$111.40	$111.40
7 purchase totals =	$642.51		$700.1478	$700.17	$700.20	$700.10