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	$24.69	12.532%	$27.7842	$27.78	$27.80	$27.80
Purchase #2	$116.38	3.341%	$120.2683	$120.27	$120.25	$120.30
Purchase #3	$40.47	13.133%	$45.7849	$45.78	$45.80	$45.80
Purchase #4	$122.29	12.421%	$137.4796	$137.48	$137.50	$137.50
Purchase #5	$82.42	7.399%	$88.5183	$88.52	$88.50	$88.50
Purchase #6	$49.30	11.144%	$54.794	$54.79	$54.80	$54.80
Purchase #7	$136.59	4.272%	$142.4251	$142.43	$142.45	$142.40
7 purchase totals =	$572.14		$617.0544	$617.05	$617.10	$617.10