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	$120.94	5.562%	$127.6667	$127.67	$127.65	$127.70
Purchase #2	$16.58	10.423%	$18.3081	$18.31	$18.30	$18.30
Purchase #3	$80.40	10.464%	$88.8131	$88.81	$88.80	$88.80
Purchase #4	$108.35	4.426%	$113.1456	$113.15	$113.15	$113.10
Purchase #5	$173.45	11.210%	$192.8937	$192.89	$192.90	$192.90
Purchase #6	$31.29	8.408%	$33.9209	$33.92	$33.90	$33.90
Purchase #7	$28.88	8.140%	$31.2308	$31.23	$31.25	$31.20
7 purchase totals =	$559.89		$605.9789	$605.98	$605.95	$605.90