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	$32.64	5.114%	$34.3092	$34.31	$34.30	$34.30
Purchase #2	$171.54	12.814%	$193.5211	$193.52	$193.50	$193.50
Purchase #3	$72.95	13.185%	$82.5685	$82.57	$82.55	$82.60
Purchase #4	$212.39	5.642%	$224.373	$224.37	$224.35	$224.40
Purchase #5	$42.87	3.741%	$44.4738	$44.47	$44.45	$44.50
Purchase #6	$229.55	5.643%	$242.5035	$242.50	$242.50	$242.50
Purchase #7	$38.63	9.527%	$42.3103	$42.31	$42.30	$42.30
7 purchase totals =	$800.57		$864.0594	$864.05	$863.95	$864.10