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	$39.60	8.299%	$42.8864	$42.89	$42.90	$42.90
Purchase #2	$148.33	4.498%	$155.0019	$155.00	$155.00	$155.00
Purchase #3	$78.97	12.776%	$89.0592	$89.06	$89.05	$89.10
Purchase #4	$153.94	13.444%	$174.6357	$174.64	$174.65	$174.60
Purchase #5	$123.75	7.345%	$132.8394	$132.84	$132.85	$132.80
Purchase #6	$213.62	13.490%	$242.4373	$242.44	$242.45	$242.40
Purchase #7	$176.77	11.401%	$196.9235	$196.92	$196.90	$196.90
7 purchase totals =	$934.98		$1,033.7834	$1,033.79	$1,033.80	$1,033.70