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	$74.52	6.541%	$79.3944	$79.39	$79.40	$79.40
Purchase #2	$199.43	11.759%	$222.881	$222.88	$222.90	$222.90
Purchase #3	$154.40	13.679%	$175.5204	$175.52	$175.50	$175.50
Purchase #4	$80.60	6.469%	$85.814	$85.81	$85.80	$85.80
Purchase #5	$207.64	4.311%	$216.5914	$216.59	$216.60	$216.60
Purchase #6	$92.66	7.666%	$99.7633	$99.76	$99.75	$99.80
Purchase #7	$81.51	12.163%	$91.4241	$91.42	$91.40	$91.40
7 purchase totals =	$890.76		$971.3886	$971.37	$971.35	$971.40