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	$153.63	13.171%	$173.8646	$173.86	$173.85	$173.90
Purchase #2	$70.55	12.450%	$79.3335	$79.33	$79.35	$79.30
Purchase #3	$106.59	6.530%	$113.5503	$113.55	$113.55	$113.60
Purchase #4	$223.33	3.454%	$231.0438	$231.04	$231.05	$231.00
Purchase #5	$132.94	5.145%	$139.7798	$139.78	$139.80	$139.80
Purchase #6	$28.98	8.561%	$31.461	$31.46	$31.45	$31.50
Purchase #7	$64.32	11.616%	$71.7914	$71.79	$71.80	$71.80
7 purchase totals =	$780.34		$840.8244	$840.81	$840.85	$840.90