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	$31.76	3.479%	$32.8649	$32.86	$32.85	$32.90
Purchase #2	$31.74	7.685%	$34.1792	$34.18	$34.20	$34.20
Purchase #3	$189.61	10.416%	$209.3598	$209.36	$209.35	$209.40
Purchase #4	$156.61	10.286%	$172.7189	$172.72	$172.70	$172.70
Purchase #5	$214.73	7.703%	$231.2707	$231.27	$231.25	$231.30
Purchase #6	$100.77	7.580%	$108.4084	$108.41	$108.40	$108.40
Purchase #7	$222.37	9.392%	$243.255	$243.26	$243.25	$243.30
7 purchase totals =	$947.59		$1,032.0569	$1,032.06	$1,032.00	$1,032.20