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	$210.39	6.124%	$223.2743	$223.27	$223.25	$223.30
Purchase #2	$127.51	10.382%	$140.7481	$140.75	$140.75	$140.70
Purchase #3	$140.72	11.511%	$156.9183	$156.92	$156.90	$156.90
Purchase #4	$101.62	10.421%	$112.2098	$112.21	$112.20	$112.20
Purchase #5	$30.51	10.729%	$33.7834	$33.78	$33.80	$33.80
Purchase #6	$158.60	8.542%	$172.1476	$172.15	$172.15	$172.10
Purchase #7	$119.98	12.325%	$134.7675	$134.77	$134.75	$134.80
7 purchase totals =	$889.33		$973.8490	$973.85	$973.80	$973.80