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	$42.84	5.661%	$45.2652	$45.27	$45.25	$45.30
Purchase #2	$38.35	9.536%	$42.0071	$42.01	$42.00	$42.00
Purchase #3	$205.27	6.379%	$218.3642	$218.36	$218.35	$218.40
Purchase #4	$49.64	9.655%	$54.4327	$54.43	$54.45	$54.40
Purchase #5	$166.72	11.290%	$185.5427	$185.54	$185.55	$185.50
Purchase #6	$124.47	7.116%	$133.3273	$133.33	$133.35	$133.30
Purchase #7	$7.33	4.454%	$7.6565	$7.66	$7.65	$7.70
7 purchase totals =	$634.62		$686.5957	$686.60	$686.60	$686.60