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	$141.82	12.335%	$159.3135	$159.31	$159.30	$159.30
Purchase #2	$142.73	5.718%	$150.8913	$150.89	$150.90	$150.90
Purchase #3	$52.79	13.102%	$59.7065	$59.71	$59.70	$59.70
Purchase #4	$139.66	5.750%	$147.6905	$147.69	$147.70	$147.70
Purchase #5	$167.28	7.463%	$179.7641	$179.76	$179.75	$179.80
Purchase #6	$217.80	5.171%	$229.0624	$229.06	$229.05	$229.10
Purchase #7	$19.60	8.255%	$21.218	$21.22	$21.20	$21.20
7 purchase totals =	$881.68		$947.6463	$947.64	$947.60	$947.70