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	$19.40	5.420%	$20.4515	$20.45	$20.45	$20.50
Purchase #2	$222.42	6.129%	$236.0521	$236.05	$236.05	$236.10
Purchase #3	$110.52	13.649%	$125.6049	$125.60	$125.60	$125.60
Purchase #4	$181.43	8.133%	$196.1857	$196.19	$196.20	$196.20
Purchase #5	$71.78	9.552%	$78.6364	$78.64	$78.65	$78.60
Purchase #6	$53.93	3.330%	$55.7259	$55.73	$55.75	$55.70
Purchase #7	$152.68	11.275%	$169.8947	$169.89	$169.90	$169.90
7 purchase totals =	$812.16		$882.5512	$882.55	$882.60	$882.60