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	$133.55	12.244%	$149.9019	$149.90	$149.90	$149.90
Purchase #2	$115.94	6.525%	$123.5051	$123.51	$123.50	$123.50
Purchase #3	$136.83	9.747%	$150.1668	$150.17	$150.15	$150.20
Purchase #4	$29.60	9.743%	$32.4839	$32.48	$32.50	$32.50
Purchase #5	$75.90	6.692%	$80.9792	$80.98	$81.00	$81.00
Purchase #6	$141.55	3.550%	$146.575	$146.58	$146.60	$146.60
Purchase #7	$73.86	12.695%	$83.2365	$83.24	$83.25	$83.20
7 purchase totals =	$707.23		$766.8484	$766.86	$766.90	$766.90