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	$50.37	9.172%	$54.9899	$54.99	$55.00	$55.00
Purchase #2	$16.63	10.211%	$18.3281	$18.33	$18.35	$18.30
Purchase #3	$76.38	8.122%	$82.5836	$82.58	$82.60	$82.60
Purchase #4	$95.71	9.527%	$104.8283	$104.83	$104.85	$104.80
Purchase #5	$111.76	7.545%	$120.1923	$120.19	$120.20	$120.20
Purchase #6	$54.74	8.853%	$59.5861	$59.59	$59.60	$59.60
Purchase #7	$17.46	6.539%	$18.6017	$18.60	$18.60	$18.60
7 purchase totals =	$423.05		$459.1100	$459.11	$459.20	$459.10