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	$36.99	3.803%	$38.3967	$38.40	$38.40	$38.40
Purchase #2	$72.82	6.545%	$77.5861	$77.59	$77.60	$77.60
Purchase #3	$21.53	12.556%	$24.2333	$24.23	$24.25	$24.20
Purchase #4	$71.54	9.661%	$78.4515	$78.45	$78.45	$78.50
Purchase #5	$170.28	5.294%	$179.2946	$179.29	$179.30	$179.30
Purchase #6	$92.35	13.346%	$104.675	$104.68	$104.70	$104.70
Purchase #7	$89.92	12.696%	$101.3362	$101.34	$101.35	$101.30
7 purchase totals =	$555.43		$603.9734	$603.98	$604.05	$604.00