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	$91.90	9.208%	$100.3622	$100.36	$100.35	$100.40
Purchase #2	$112.58	13.236%	$127.4811	$127.48	$127.50	$127.50
Purchase #3	$111.27	5.860%	$117.7904	$117.79	$117.80	$117.80
Purchase #4	$86.87	4.866%	$91.0971	$91.10	$91.10	$91.10
Purchase #5	$86.63	4.361%	$90.4079	$90.41	$90.40	$90.40
Purchase #6	$48.44	3.676%	$50.2207	$50.22	$50.20	$50.20
Purchase #7	$212.64	11.553%	$237.2063	$237.21	$237.20	$237.20
7 purchase totals =	$750.33		$814.5657	$814.57	$814.55	$814.60