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	$242.25	11.816%	$270.8743	$270.87	$270.85	$270.90
Purchase #2	$109.43	10.829%	$121.2802	$121.28	$121.30	$121.30
Purchase #3	$123.88	5.500%	$130.6934	$130.69	$130.70	$130.70
Purchase #4	$63.66	6.406%	$67.7381	$67.74	$67.75	$67.70
Purchase #5	$38.33	9.498%	$41.9706	$41.97	$41.95	$42.00
Purchase #6	$132.72	11.105%	$147.4586	$147.46	$147.45	$147.50
Purchase #7	$223.66	6.619%	$238.4641	$238.46	$238.45	$238.50
7 purchase totals =	$933.93		$1,018.4793	$1,018.47	$1,018.45	$1,018.60