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	$246.41	4.140%	$256.6114	$256.61	$256.60	$256.60
Purchase #2	$183.42	9.837%	$201.463	$201.46	$201.45	$201.50
Purchase #3	$229.71	6.640%	$244.9627	$244.96	$244.95	$245.00
Purchase #4	$188.85	6.344%	$200.8306	$200.83	$200.85	$200.80
Purchase #5	$194.31	3.374%	$200.866	$200.87	$200.85	$200.90
Purchase #6	$116.69	7.641%	$125.6063	$125.61	$125.60	$125.60
Purchase #7	$82.99	9.369%	$90.7653	$90.77	$90.75	$90.80
7 purchase totals =	$1,242.38		$1,321.1053	$1,321.11	$1,321.05	$1,321.20