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	$42.46	6.394%	$45.1749	$45.17	$45.15	$45.20
Purchase #2	$32.44	3.498%	$33.5748	$33.57	$33.55	$33.60
Purchase #3	$51.86	11.490%	$57.8187	$57.82	$57.80	$57.80
Purchase #4	$238.41	7.860%	$257.149	$257.15	$257.15	$257.10
Purchase #5	$30.88	12.175%	$34.6396	$34.64	$34.65	$34.60
Purchase #6	$100.63	3.227%	$103.8773	$103.88	$103.90	$103.90
Purchase #7	$103.83	10.125%	$114.3428	$114.34	$114.35	$114.30
7 purchase totals =	$600.51		$646.5771	$646.57	$646.55	$646.50