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	$80.34	11.368%	$89.4731	$89.47	$89.45	$89.50
Purchase #2	$21.81	13.790%	$24.8176	$24.82	$24.80	$24.80
Purchase #3	$212.30	9.515%	$232.5003	$232.50	$232.50	$232.50
Purchase #4	$91.94	10.225%	$101.3409	$101.34	$101.35	$101.30
Purchase #5	$75.78	13.559%	$86.055	$86.06	$86.05	$86.10
Purchase #6	$207.94	4.162%	$216.5945	$216.59	$216.60	$216.60
Purchase #7	$75.74	4.103%	$78.8476	$78.85	$78.85	$78.80
7 purchase totals =	$765.85		$829.6290	$829.63	$829.60	$829.60