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	$101.57	3.514%	$105.1392	$105.14	$105.15	$105.10
Purchase #2	$47.54	12.559%	$53.5105	$53.51	$53.50	$53.50
Purchase #3	$149.48	4.642%	$156.4189	$156.42	$156.40	$156.40
Purchase #4	$143.52	11.739%	$160.3678	$160.37	$160.35	$160.40
Purchase #5	$100.58	3.157%	$103.7553	$103.76	$103.75	$103.80
Purchase #6	$24.93	12.242%	$27.9819	$27.98	$28.00	$28.00
Purchase #7	$229.94	9.127%	$250.9266	$250.93	$250.95	$250.90
7 purchase totals =	$797.56		$858.1002	$858.11	$858.10	$858.10