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	$91.25	10.402%	$100.7418	$100.74	$100.75	$100.70
Purchase #2	$161.44	9.398%	$176.6121	$176.61	$176.60	$176.60
Purchase #3	$162.92	6.109%	$172.8728	$172.87	$172.85	$172.90
Purchase #4	$134.27	7.426%	$144.2409	$144.24	$144.25	$144.20
Purchase #5	$76.81	12.297%	$86.2553	$86.26	$86.25	$86.30
Purchase #6	$131.52	8.302%	$142.4388	$142.44	$142.45	$142.40
Purchase #7	$31.79	8.831%	$34.5974	$34.60	$34.60	$34.60
7 purchase totals =	$790.00		$857.7591	$857.76	$857.75	$857.70