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	$232.84	7.706%	$250.7827	$250.78	$250.80	$250.80
Purchase #2	$68.95	13.826%	$78.483	$78.48	$78.50	$78.50
Purchase #3	$231.78	9.214%	$253.1362	$253.14	$253.15	$253.10
Purchase #4	$96.29	4.104%	$100.2417	$100.24	$100.25	$100.20
Purchase #5	$169.57	6.726%	$180.9753	$180.98	$181.00	$181.00
Purchase #6	$155.31	10.264%	$171.251	$171.25	$171.25	$171.30
Purchase #7	$193.27	9.246%	$211.1397	$211.14	$211.15	$211.10
7 purchase totals =	$1,148.01		$1,246.0096	$1,246.01	$1,246.10	$1,246.00