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	$39.27	11.698%	$43.8638	$43.86	$43.85	$43.90
Purchase #2	$112.92	9.822%	$124.011	$124.01	$124.00	$124.00
Purchase #3	$84.52	9.245%	$92.3339	$92.33	$92.35	$92.30
Purchase #4	$192.30	11.758%	$214.9106	$214.91	$214.90	$214.90
Purchase #5	$65.36	9.281%	$71.4261	$71.43	$71.45	$71.40
Purchase #6	$87.66	7.500%	$94.2345	$94.23	$94.25	$94.20
Purchase #7	$30.52	10.114%	$33.6068	$33.61	$33.60	$33.60
7 purchase totals =	$612.55		$674.3867	$674.38	$674.40	$674.30