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	$206.81	10.237%	$227.9811	$227.98	$228.00	$228.00
Purchase #2	$187.28	8.568%	$203.3262	$203.33	$203.35	$203.30
Purchase #3	$127.78	11.310%	$142.2319	$142.23	$142.25	$142.20
Purchase #4	$79.55	7.256%	$85.3221	$85.32	$85.30	$85.30
Purchase #5	$159.26	8.796%	$173.2685	$173.27	$173.25	$173.30
Purchase #6	$19.33	11.625%	$21.5771	$21.58	$21.60	$21.60
Purchase #7	$177.95	4.304%	$185.609	$185.61	$185.60	$185.60
7 purchase totals =	$957.96		$1,039.3159	$1,039.32	$1,039.35	$1,039.30