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	$205.55	12.473%	$231.1883	$231.19	$231.20	$231.20
Purchase #2	$55.82	10.225%	$61.5276	$61.53	$61.55	$61.50
Purchase #3	$159.88	8.311%	$173.1676	$173.17	$173.15	$173.20
Purchase #4	$206.27	8.824%	$224.4713	$224.47	$224.45	$224.50
Purchase #5	$95.69	10.654%	$105.8848	$105.88	$105.90	$105.90
Purchase #6	$40.87	11.696%	$45.6502	$45.65	$45.65	$45.70
Purchase #7	$151.52	7.109%	$162.2916	$162.29	$162.30	$162.30
7 purchase totals =	$915.60		$1,004.1814	$1,004.18	$1,004.20	$1,004.30