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	$79.33	13.835%	$90.3053	$90.31	$90.30	$90.30
Purchase #2	$91.99	12.146%	$103.1631	$103.16	$103.15	$103.20
Purchase #3	$64.41	5.520%	$67.9654	$67.97	$67.95	$68.00
Purchase #4	$83.65	3.443%	$86.5301	$86.53	$86.55	$86.50
Purchase #5	$192.40	3.380%	$198.9031	$198.90	$198.90	$198.90
Purchase #6	$112.96	10.303%	$124.5983	$124.60	$124.60	$124.60
Purchase #7	$38.46	13.716%	$43.7352	$43.74	$43.75	$43.70
7 purchase totals =	$663.20		$715.2005	$715.21	$715.20	$715.20