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	$185.94	11.123%	$206.6221	$206.62	$206.60	$206.60
Purchase #2	$240.84	13.737%	$273.9242	$273.92	$273.90	$273.90
Purchase #3	$228.48	13.179%	$258.5914	$258.59	$258.60	$258.60
Purchase #4	$101.60	9.777%	$111.5334	$111.53	$111.55	$111.50
Purchase #5	$173.25	6.764%	$184.9686	$184.97	$184.95	$185.00
Purchase #6	$156.27	9.517%	$171.1422	$171.14	$171.15	$171.10
Purchase #7	$37.42	7.188%	$40.1097	$40.11	$40.10	$40.10
7 purchase totals =	$1,123.80		$1,246.8916	$1,246.88	$1,246.85	$1,246.80