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	$52.54	9.843%	$57.7115	$57.71	$57.70	$57.70
Purchase #2	$109.63	10.287%	$120.9076	$120.91	$120.90	$120.90
Purchase #3	$164.81	6.170%	$174.9788	$174.98	$175.00	$175.00
Purchase #4	$50.39	4.378%	$52.5961	$52.60	$52.60	$52.60
Purchase #5	$133.61	6.634%	$142.4737	$142.47	$142.45	$142.50
Purchase #6	$116.87	12.342%	$131.2941	$131.29	$131.30	$131.30
Purchase #7	$144.69	10.459%	$159.8231	$159.82	$159.80	$159.80
7 purchase totals =	$772.54		$839.7849	$839.78	$839.75	$839.80