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	$126.25	6.315%	$134.2227	$134.22	$134.20	$134.20
Purchase #2	$103.38	12.109%	$115.8983	$115.90	$115.90	$115.90
Purchase #3	$80.76	11.444%	$90.0022	$90.00	$90.00	$90.00
Purchase #4	$88.68	11.822%	$99.1637	$99.16	$99.15	$99.20
Purchase #5	$182.55	4.453%	$190.679	$190.68	$190.70	$190.70
Purchase #6	$118.32	13.569%	$134.3748	$134.37	$134.35	$134.40
Purchase #7	$88.41	7.480%	$95.0231	$95.02	$95.00	$95.00
7 purchase totals =	$788.35		$859.3638	$859.35	$859.30	$859.40