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	$82.30	12.768%	$92.8081	$92.81	$92.80	$92.80
Purchase #2	$54.46	9.722%	$59.7546	$59.75	$59.75	$59.80
Purchase #3	$25.31	11.679%	$28.266	$28.27	$28.25	$28.30
Purchase #4	$100.60	10.495%	$111.158	$111.16	$111.15	$111.20
Purchase #5	$180.83	9.681%	$198.3362	$198.34	$198.35	$198.30
Purchase #6	$155.48	3.422%	$160.8005	$160.80	$160.80	$160.80
Purchase #7	$13.90	9.417%	$15.209	$15.21	$15.20	$15.20
7 purchase totals =	$612.88		$666.3324	$666.34	$666.30	$666.40