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	$183.47	6.701%	$195.7643	$195.76	$195.75	$195.80
Purchase #2	$206.47	11.677%	$230.5795	$230.58	$230.60	$230.60
Purchase #3	$196.91	10.782%	$218.1408	$218.14	$218.15	$218.10
Purchase #4	$54.28	10.240%	$59.8383	$59.84	$59.85	$59.80
Purchase #5	$78.94	12.502%	$88.8091	$88.81	$88.80	$88.80
Purchase #6	$151.69	12.654%	$170.8849	$170.88	$170.90	$170.90
Purchase #7	$132.80	4.745%	$139.1014	$139.10	$139.10	$139.10
7 purchase totals =	$1,004.56		$1,103.1183	$1,103.11	$1,103.15	$1,103.10