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	$23.60	6.612%	$25.1604	$25.16	$25.15	$25.20
Purchase #2	$71.50	9.793%	$78.502	$78.50	$78.50	$78.50
Purchase #3	$212.80	3.132%	$219.4649	$219.46	$219.45	$219.50
Purchase #4	$15.97	10.163%	$17.593	$17.59	$17.60	$17.60
Purchase #5	$247.60	5.778%	$261.9063	$261.91	$261.90	$261.90
Purchase #6	$243.39	11.234%	$270.7324	$270.73	$270.75	$270.70
Purchase #7	$22.27	10.215%	$24.5449	$24.54	$24.55	$24.50
7 purchase totals =	$837.13		$897.9039	$897.89	$897.90	$897.90