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	$81.93	8.792%	$89.1333	$89.13	$89.15	$89.10
Purchase #2	$53.58	10.773%	$59.3522	$59.35	$59.35	$59.40
Purchase #3	$250.71	4.332%	$261.5708	$261.57	$261.55	$261.60
Purchase #4	$247.83	10.294%	$273.3416	$273.34	$273.35	$273.30
Purchase #5	$184.32	3.106%	$190.045	$190.05	$190.05	$190.00
Purchase #6	$157.88	10.512%	$174.4763	$174.48	$174.50	$174.50
Purchase #7	$142.84	5.509%	$150.7091	$150.71	$150.70	$150.70
7 purchase totals =	$1,119.09		$1,198.6283	$1,198.63	$1,198.65	$1,198.60