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	$85.36	6.433%	$90.8512	$90.85	$90.85	$90.90
Purchase #2	$142.41	6.493%	$151.6567	$151.66	$151.65	$151.70
Purchase #3	$212.89	8.788%	$231.5988	$231.60	$231.60	$231.60
Purchase #4	$61.55	12.303%	$69.1225	$69.12	$69.10	$69.10
Purchase #5	$190.58	10.638%	$210.8539	$210.85	$210.85	$210.90
Purchase #6	$110.43	11.767%	$123.4243	$123.42	$123.40	$123.40
Purchase #7	$207.69	6.607%	$221.4121	$221.41	$221.40	$221.40
7 purchase totals =	$1,010.91		$1,098.9195	$1,098.91	$1,098.85	$1,099.00