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	$12.77	5.121%	$13.424	$13.42	$13.40	$13.40
Purchase #2	$114.97	10.756%	$127.3362	$127.34	$127.35	$127.30
Purchase #3	$220.93	4.795%	$231.5236	$231.52	$231.50	$231.50
Purchase #4	$167.61	10.466%	$185.1521	$185.15	$185.15	$185.20
Purchase #5	$11.33	13.778%	$12.891	$12.89	$12.90	$12.90
Purchase #6	$186.37	12.234%	$209.1705	$209.17	$209.15	$209.20
Purchase #7	$5.41	9.560%	$5.9272	$5.93	$5.95	$5.90
7 purchase totals =	$719.39		$785.4246	$785.42	$785.40	$785.40