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	$59.94	6.287%	$63.7084	$63.71	$63.70	$63.70
Purchase #2	$49.30	6.456%	$52.4828	$52.48	$52.50	$52.50
Purchase #3	$180.56	4.437%	$188.5714	$188.57	$188.55	$188.60
Purchase #4	$105.54	11.228%	$117.39	$117.39	$117.40	$117.40
Purchase #5	$132.88	11.769%	$148.5186	$148.52	$148.50	$148.50
Purchase #6	$110.57	5.155%	$116.2699	$116.27	$116.25	$116.30
Purchase #7	$121.76	9.457%	$133.2748	$133.27	$133.25	$133.30
7 purchase totals =	$760.55		$820.2159	$820.21	$820.15	$820.30