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	$156.69	7.299%	$168.1268	$168.13	$168.15	$168.10
Purchase #2	$81.33	12.689%	$91.65	$91.65	$91.65	$91.70
Purchase #3	$49.62	4.468%	$51.837	$51.84	$51.85	$51.80
Purchase #4	$40.65	12.704%	$45.8142	$45.81	$45.80	$45.80
Purchase #5	$71.50	12.696%	$80.5776	$80.58	$80.60	$80.60
Purchase #6	$115.38	7.402%	$123.9204	$123.92	$123.90	$123.90
Purchase #7	$37.68	12.180%	$42.2694	$42.27	$42.25	$42.30
7 purchase totals =	$552.85		$604.1954	$604.20	$604.20	$604.20