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	$213.60	12.638%	$240.5948	$240.59	$240.60	$240.60
Purchase #2	$100.69	10.512%	$111.2745	$111.27	$111.25	$111.30
Purchase #3	$82.95	3.392%	$85.7637	$85.76	$85.75	$85.80
Purchase #4	$6.71	3.146%	$6.9211	$6.92	$6.90	$6.90
Purchase #5	$212.63	7.159%	$227.8522	$227.85	$227.85	$227.90
Purchase #6	$84.30	10.548%	$93.192	$93.19	$93.20	$93.20
Purchase #7	$222.45	4.766%	$233.052	$233.05	$233.05	$233.10
7 purchase totals =	$923.33		$998.6503	$998.63	$998.60	$998.80