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	$206.35	8.295%	$223.4667	$223.47	$223.45	$223.50
Purchase #2	$18.33	9.549%	$20.0803	$20.08	$20.10	$20.10
Purchase #3	$91.54	5.509%	$96.5829	$96.58	$96.60	$96.60
Purchase #4	$25.89	13.220%	$29.3127	$29.31	$29.30	$29.30
Purchase #5	$245.95	10.776%	$272.4536	$272.45	$272.45	$272.50
Purchase #6	$130.61	7.581%	$140.5115	$140.51	$140.50	$140.50
Purchase #7	$21.29	13.106%	$24.0803	$24.08	$24.10	$24.10
7 purchase totals =	$739.96		$806.4880	$806.48	$806.50	$806.60