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	$56.81	4.727%	$59.4954	$59.50	$59.50	$59.50
Purchase #2	$30.80	10.435%	$34.014	$34.01	$34.00	$34.00
Purchase #3	$201.42	13.375%	$228.3599	$228.36	$228.35	$228.40
Purchase #4	$185.31	5.165%	$194.8813	$194.88	$194.90	$194.90
Purchase #5	$7.29	8.546%	$7.913	$7.91	$7.90	$7.90
Purchase #6	$46.49	8.237%	$50.3194	$50.32	$50.30	$50.30
Purchase #7	$5.66	3.832%	$5.8769	$5.88	$5.90	$5.90
7 purchase totals =	$533.78		$580.8599	$580.86	$580.85	$580.90