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	$228.94	12.487%	$257.5277	$257.53	$257.55	$257.50
Purchase #2	$18.34	9.846%	$20.1458	$20.15	$20.15	$20.10
Purchase #3	$126.82	12.269%	$142.3795	$142.38	$142.40	$142.40
Purchase #4	$84.40	7.308%	$90.568	$90.57	$90.55	$90.60
Purchase #5	$39.95	13.817%	$45.4699	$45.47	$45.45	$45.50
Purchase #6	$231.56	13.707%	$263.2999	$263.30	$263.30	$263.30
Purchase #7	$58.86	3.359%	$60.8371	$60.84	$60.85	$60.80
7 purchase totals =	$788.87		$880.2279	$880.24	$880.25	$880.20