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	$84.88	5.766%	$89.7742	$89.77	$89.75	$89.80
Purchase #2	$180.25	10.107%	$198.4679	$198.47	$198.45	$198.50
Purchase #3	$39.25	7.227%	$42.0866	$42.09	$42.10	$42.10
Purchase #4	$198.34	11.815%	$221.7739	$221.77	$221.75	$221.80
Purchase #5	$141.87	12.511%	$159.6194	$159.62	$159.60	$159.60
Purchase #6	$85.74	3.367%	$88.6269	$88.63	$88.65	$88.60
Purchase #7	$33.41	4.417%	$34.8857	$34.89	$34.90	$34.90
7 purchase totals =	$763.74		$835.2346	$835.24	$835.20	$835.30