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	$172.34	10.176%	$189.8773	$189.88	$189.90	$189.90
Purchase #2	$222.89	9.838%	$244.8179	$244.82	$244.80	$244.80
Purchase #3	$192.91	13.315%	$218.596	$218.60	$218.60	$218.60
Purchase #4	$47.85	5.608%	$50.5334	$50.53	$50.55	$50.50
Purchase #5	$57.53	3.601%	$59.6017	$59.60	$59.60	$59.60
Purchase #6	$104.87	9.229%	$114.5485	$114.55	$114.55	$114.50
Purchase #7	$97.57	13.550%	$110.7907	$110.79	$110.80	$110.80
7 purchase totals =	$895.96		$988.7655	$988.77	$988.80	$988.70