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	$98.65	3.288%	$101.8936	$101.89	$101.90	$101.90
Purchase #2	$151.27	13.831%	$172.1922	$172.19	$172.20	$172.20
Purchase #3	$212.90	3.614%	$220.5942	$220.59	$220.60	$220.60
Purchase #4	$113.31	5.610%	$119.6667	$119.67	$119.65	$119.70
Purchase #5	$216.81	9.810%	$238.0791	$238.08	$238.10	$238.10
Purchase #6	$82.26	9.801%	$90.3223	$90.32	$90.30	$90.30
Purchase #7	$32.48	10.688%	$35.9515	$35.95	$35.95	$36.00
7 purchase totals =	$907.68		$978.6996	$978.69	$978.70	$978.80