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	$246.46	12.308%	$276.7943	$276.79	$276.80	$276.80
Purchase #2	$45.55	8.444%	$49.3962	$49.40	$49.40	$49.40
Purchase #3	$36.59	3.517%	$37.8769	$37.88	$37.90	$37.90
Purchase #4	$237.42	9.152%	$259.1487	$259.15	$259.15	$259.10
Purchase #5	$80.54	4.151%	$83.8832	$83.88	$83.90	$83.90
Purchase #6	$13.93	4.567%	$14.5662	$14.57	$14.55	$14.60
Purchase #7	$77.67	11.439%	$86.5547	$86.55	$86.55	$86.60
7 purchase totals =	$738.16		$808.2202	$808.22	$808.25	$808.30