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	$119.94	6.550%	$127.7961	$127.80	$127.80	$127.80
Purchase #2	$112.27	4.699%	$117.5456	$117.55	$117.55	$117.50
Purchase #3	$47.25	8.716%	$51.3683	$51.37	$51.35	$51.40
Purchase #4	$116.46	12.646%	$131.1875	$131.19	$131.20	$131.20
Purchase #5	$7.77	10.151%	$8.5587	$8.56	$8.55	$8.60
Purchase #6	$140.35	8.184%	$151.8362	$151.84	$151.85	$151.80
Purchase #7	$206.47	4.700%	$216.1741	$216.17	$216.15	$216.20
7 purchase totals =	$750.51		$804.4665	$804.48	$804.45	$804.50