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	$177.46	4.413%	$185.2913	$185.29	$185.30	$185.30
Purchase #2	$28.90	13.340%	$32.7553	$32.76	$32.75	$32.80
Purchase #3	$81.45	10.452%	$89.9632	$89.96	$89.95	$90.00
Purchase #4	$107.96	7.733%	$116.3085	$116.31	$116.30	$116.30
Purchase #5	$222.84	6.304%	$236.8878	$236.89	$236.90	$236.90
Purchase #6	$145.97	5.843%	$154.499	$154.50	$154.50	$154.50
Purchase #7	$130.68	3.763%	$135.5975	$135.60	$135.60	$135.60
7 purchase totals =	$895.26		$951.3026	$951.31	$951.30	$951.40