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	$55.60	7.285%	$59.6505	$59.65	$59.65	$59.70
Purchase #2	$185.73	5.598%	$196.1272	$196.13	$196.15	$196.10
Purchase #3	$111.88	11.356%	$124.5851	$124.59	$124.60	$124.60
Purchase #4	$23.70	9.370%	$25.9207	$25.92	$25.90	$25.90
Purchase #5	$141.83	3.184%	$146.3459	$146.35	$146.35	$146.30
Purchase #6	$6.94	5.625%	$7.3304	$7.33	$7.35	$7.30
Purchase #7	$225.88	13.858%	$257.1825	$257.18	$257.20	$257.20
7 purchase totals =	$751.56		$817.1423	$817.15	$817.20	$817.10