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	$149.45	10.619%	$165.3201	$165.32	$165.30	$165.30
Purchase #2	$179.59	9.480%	$196.6151	$196.62	$196.60	$196.60
Purchase #3	$54.70	5.138%	$57.5105	$57.51	$57.50	$57.50
Purchase #4	$232.81	7.648%	$250.6153	$250.62	$250.60	$250.60
Purchase #5	$28.55	9.138%	$31.1589	$31.16	$31.15	$31.20
Purchase #6	$71.85	13.479%	$81.5347	$81.53	$81.55	$81.50
Purchase #7	$228.29	8.205%	$247.0212	$247.02	$247.00	$247.00
7 purchase totals =	$945.24		$1,029.7758	$1,029.78	$1,029.70	$1,029.70