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	$172.51	9.212%	$188.4016	$188.40	$188.40	$188.40
Purchase #2	$11.86	5.658%	$12.531	$12.53	$12.55	$12.50
Purchase #3	$98.89	11.664%	$110.4245	$110.42	$110.40	$110.40
Purchase #4	$88.59	12.402%	$99.5769	$99.58	$99.60	$99.60
Purchase #5	$117.68	8.231%	$127.3662	$127.37	$127.35	$127.40
Purchase #6	$102.36	10.251%	$112.8529	$112.85	$112.85	$112.90
Purchase #7	$218.57	9.296%	$238.8883	$238.89	$238.90	$238.90
7 purchase totals =	$810.46		$890.0414	$890.04	$890.05	$890.10