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	$91.56	3.123%	$94.4194	$94.42	$94.40	$94.40
Purchase #2	$143.84	11.413%	$160.2565	$160.26	$160.25	$160.30
Purchase #3	$160.54	8.549%	$174.2646	$174.26	$174.25	$174.30
Purchase #4	$235.64	10.760%	$260.9949	$260.99	$261.00	$261.00
Purchase #5	$140.37	7.509%	$150.9104	$150.91	$150.90	$150.90
Purchase #6	$42.31	6.605%	$45.1046	$45.10	$45.10	$45.10
Purchase #7	$222.87	12.567%	$250.8781	$250.88	$250.90	$250.90
7 purchase totals =	$1,037.13		$1,136.8285	$1,136.82	$1,136.80	$1,136.90