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	$72.53	8.703%	$78.8423	$78.84	$78.85	$78.80
Purchase #2	$121.25	8.113%	$131.087	$131.09	$131.10	$131.10
Purchase #3	$245.34	10.667%	$271.5104	$271.51	$271.50	$271.50
Purchase #4	$92.35	4.221%	$96.2481	$96.25	$96.25	$96.20
Purchase #5	$238.34	9.342%	$260.6057	$260.61	$260.60	$260.60
Purchase #6	$90.54	11.131%	$100.618	$100.62	$100.60	$100.60
Purchase #7	$41.63	8.706%	$45.2543	$45.25	$45.25	$45.30
7 purchase totals =	$901.98		$984.1658	$984.17	$984.15	$984.10