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	$11.80	13.164%	$13.3534	$13.35	$13.35	$13.40
Purchase #2	$37.74	12.472%	$42.4469	$42.45	$42.45	$42.40
Purchase #3	$56.75	4.611%	$59.3667	$59.37	$59.35	$59.40
Purchase #4	$159.25	7.740%	$171.576	$171.58	$171.60	$171.60
Purchase #5	$226.69	5.480%	$239.1126	$239.11	$239.10	$239.10
Purchase #6	$128.85	4.247%	$134.3223	$134.32	$134.30	$134.30
Purchase #7	$222.36	10.840%	$246.4638	$246.46	$246.45	$246.50
7 purchase totals =	$843.44		$906.6417	$906.64	$906.60	$906.70