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	$70.47	12.679%	$79.4049	$79.40	$79.40	$79.40
Purchase #2	$95.88	4.856%	$100.5359	$100.54	$100.55	$100.50
Purchase #3	$30.51	9.736%	$33.4805	$33.48	$33.50	$33.50
Purchase #4	$89.83	7.298%	$96.3858	$96.39	$96.40	$96.40
Purchase #5	$209.71	4.351%	$218.8345	$218.83	$218.85	$218.80
Purchase #6	$176.37	9.136%	$192.4832	$192.48	$192.50	$192.50
Purchase #7	$207.80	10.570%	$229.7645	$229.76	$229.75	$229.80
7 purchase totals =	$880.57		$950.8893	$950.88	$950.95	$950.90