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	$246.58	9.747%	$270.6142	$270.61	$270.60	$270.60
Purchase #2	$37.42	6.456%	$39.8358	$39.84	$39.85	$39.80
Purchase #3	$159.96	10.689%	$177.0581	$177.06	$177.05	$177.10
Purchase #4	$78.57	4.757%	$82.3076	$82.31	$82.30	$82.30
Purchase #5	$203.54	5.800%	$215.3453	$215.35	$215.35	$215.30
Purchase #6	$125.69	13.288%	$142.3917	$142.39	$142.40	$142.40
Purchase #7	$88.41	4.657%	$92.5273	$92.53	$92.55	$92.50
7 purchase totals =	$940.17		$1,020.0800	$1,020.09	$1,020.10	$1,020.00