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	$21.99	10.347%	$24.2653	$24.27	$24.25	$24.30
Purchase #2	$47.32	6.690%	$50.4857	$50.49	$50.50	$50.50
Purchase #3	$250.43	7.822%	$270.0186	$270.02	$270.00	$270.00
Purchase #4	$175.38	5.635%	$185.2627	$185.26	$185.25	$185.30
Purchase #5	$220.59	13.498%	$250.3652	$250.37	$250.35	$250.40
Purchase #6	$55.50	7.210%	$59.5016	$59.50	$59.50	$59.50
Purchase #7	$160.49	11.248%	$178.5419	$178.54	$178.55	$178.50
7 purchase totals =	$931.70		$1,018.4410	$1,018.45	$1,018.40	$1,018.50