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	$66.74	5.241%	$70.2378	$70.24	$70.25	$70.20
Purchase #2	$166.29	7.511%	$178.78	$178.78	$178.80	$178.80
Purchase #3	$62.83	5.184%	$66.0871	$66.09	$66.10	$66.10
Purchase #4	$140.57	13.307%	$159.2756	$159.28	$159.30	$159.30
Purchase #5	$170.60	5.780%	$180.4607	$180.46	$180.45	$180.50
Purchase #6	$28.94	10.106%	$31.8647	$31.86	$31.85	$31.90
Purchase #7	$221.51	7.196%	$237.4499	$237.45	$237.45	$237.40
7 purchase totals =	$857.48		$924.1558	$924.16	$924.20	$924.20