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	$234.61	8.267%	$254.0052	$254.01	$254.00	$254.00
Purchase #2	$81.58	10.202%	$89.9028	$89.90	$89.90	$89.90
Purchase #3	$117.52	9.226%	$128.3624	$128.36	$128.35	$128.40
Purchase #4	$118.90	13.118%	$134.4973	$134.50	$134.50	$134.50
Purchase #5	$58.82	6.700%	$62.7609	$62.76	$62.75	$62.80
Purchase #6	$118.96	13.315%	$134.7995	$134.80	$134.80	$134.80
Purchase #7	$50.42	4.735%	$52.8074	$52.81	$52.80	$52.80
7 purchase totals =	$780.81		$857.1355	$857.14	$857.10	$857.20