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	$141.37	8.427%	$153.2832	$153.28	$153.30	$153.30
Purchase #2	$134.29	12.231%	$150.715	$150.72	$150.70	$150.70
Purchase #3	$91.46	8.816%	$99.5231	$99.52	$99.50	$99.50
Purchase #4	$42.72	3.720%	$44.3092	$44.31	$44.30	$44.30
Purchase #5	$104.96	6.671%	$111.9619	$111.96	$111.95	$112.00
Purchase #6	$35.77	5.560%	$37.7588	$37.76	$37.75	$37.80
Purchase #7	$66.39	10.614%	$73.4366	$73.44	$73.45	$73.40
7 purchase totals =	$616.96		$670.9878	$670.99	$670.95	$671.00