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	$125.28	3.748%	$129.9755	$129.98	$130.00	$130.00
Purchase #2	$134.59	3.860%	$139.7852	$139.79	$139.80	$139.80
Purchase #3	$72.75	11.200%	$80.898	$80.90	$80.90	$80.90
Purchase #4	$116.34	13.221%	$131.7213	$131.72	$131.70	$131.70
Purchase #5	$113.28	10.278%	$124.9229	$124.92	$124.90	$124.90
Purchase #6	$25.78	13.256%	$29.1974	$29.20	$29.20	$29.20
Purchase #7	$151.43	9.604%	$165.9733	$165.97	$165.95	$166.00
7 purchase totals =	$739.45		$802.4736	$802.48	$802.45	$802.50