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	$247.48	7.804%	$266.7933	$266.79	$266.80	$266.80
Purchase #2	$107.84	3.752%	$111.8862	$111.89	$111.90	$111.90
Purchase #3	$35.96	3.377%	$37.1744	$37.17	$37.15	$37.20
Purchase #4	$180.56	10.349%	$199.2462	$199.25	$199.25	$199.20
Purchase #5	$242.39	9.537%	$265.5067	$265.51	$265.50	$265.50
Purchase #6	$234.49	11.123%	$260.5723	$260.57	$260.55	$260.60
Purchase #7	$184.70	7.590%	$198.7187	$198.72	$198.70	$198.70
7 purchase totals =	$1,233.42		$1,339.8978	$1,339.90	$1,339.85	$1,339.90