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	$170.80	6.678%	$182.206	$182.21	$182.20	$182.20
Purchase #2	$34.53	8.847%	$37.5849	$37.58	$37.60	$37.60
Purchase #3	$134.68	4.223%	$140.3675	$140.37	$140.35	$140.40
Purchase #4	$128.58	12.201%	$144.268	$144.27	$144.25	$144.30
Purchase #5	$190.98	11.616%	$213.1642	$213.16	$213.15	$213.20
Purchase #6	$81.49	11.166%	$90.5892	$90.59	$90.60	$90.60
Purchase #7	$52.44	10.102%	$57.7375	$57.74	$57.75	$57.70
7 purchase totals =	$793.50		$865.9173	$865.92	$865.90	$866.00