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	$105.84	7.134%	$113.3906	$113.39	$113.40	$113.40
Purchase #2	$36.55	5.199%	$38.4502	$38.45	$38.45	$38.50
Purchase #3	$99.97	4.190%	$104.1587	$104.16	$104.15	$104.20
Purchase #4	$117.92	12.651%	$132.8381	$132.84	$132.85	$132.80
Purchase #5	$55.70	6.266%	$59.1902	$59.19	$59.20	$59.20
Purchase #6	$82.71	3.480%	$85.5883	$85.59	$85.60	$85.60
Purchase #7	$172.77	9.226%	$188.7098	$188.71	$188.70	$188.70
7 purchase totals =	$671.46		$722.3259	$722.33	$722.35	$722.40