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	$20.42	7.123%	$21.8745	$21.87	$21.85	$21.90
Purchase #2	$98.79	12.497%	$111.1358	$111.14	$111.15	$111.10
Purchase #3	$157.35	12.780%	$177.4593	$177.46	$177.45	$177.50
Purchase #4	$29.37	8.433%	$31.8468	$31.85	$31.85	$31.80
Purchase #5	$79.50	7.103%	$85.1469	$85.15	$85.15	$85.10
Purchase #6	$5.26	4.691%	$5.5067	$5.51	$5.50	$5.50
Purchase #7	$67.71	6.295%	$71.9723	$71.97	$71.95	$72.00
7 purchase totals =	$458.40		$504.9423	$504.95	$504.90	$504.90