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	$160.67	3.265%	$165.9159	$165.92	$165.90	$165.90
Purchase #2	$50.50	10.382%	$55.7429	$55.74	$55.75	$55.70
Purchase #3	$117.32	9.605%	$128.5886	$128.59	$128.60	$128.60
Purchase #4	$47.50	8.500%	$51.5375	$51.54	$51.55	$51.50
Purchase #5	$147.44	3.308%	$152.3173	$152.32	$152.30	$152.30
Purchase #6	$227.76	4.460%	$237.9181	$237.92	$237.90	$237.90
Purchase #7	$19.41	11.184%	$21.5808	$21.58	$21.60	$21.60
7 purchase totals =	$770.60		$813.6011	$813.61	$813.60	$813.50