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	$242.60	4.665%	$253.9173	$253.92	$253.90	$253.90
Purchase #2	$102.78	10.834%	$113.9152	$113.92	$113.90	$113.90
Purchase #3	$59.91	4.317%	$62.4963	$62.50	$62.50	$62.50
Purchase #4	$119.40	11.436%	$133.0546	$133.05	$133.05	$133.10
Purchase #5	$42.53	8.309%	$46.0638	$46.06	$46.05	$46.10
Purchase #6	$69.38	12.330%	$77.9346	$77.93	$77.95	$77.90
Purchase #7	$43.66	3.413%	$45.1501	$45.15	$45.15	$45.20
7 purchase totals =	$680.26		$732.5319	$732.53	$732.50	$732.60