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	$125.29	12.663%	$141.1555	$141.16	$141.15	$141.20
Purchase #2	$207.65	8.486%	$225.2712	$225.27	$225.25	$225.30
Purchase #3	$225.52	6.789%	$240.8306	$240.83	$240.85	$240.80
Purchase #4	$23.35	10.823%	$25.8772	$25.88	$25.90	$25.90
Purchase #5	$143.95	8.472%	$156.1454	$156.15	$156.15	$156.10
Purchase #6	$173.56	10.370%	$191.5582	$191.56	$191.55	$191.60
Purchase #7	$172.70	10.802%	$191.3551	$191.36	$191.35	$191.40
7 purchase totals =	$1,072.02		$1,172.1932	$1,172.21	$1,172.20	$1,172.30