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	$97.58	3.598%	$101.0909	$101.09	$101.10	$101.10
Purchase #2	$153.39	9.231%	$167.5494	$167.55	$167.55	$167.50
Purchase #3	$51.98	11.868%	$58.149	$58.15	$58.15	$58.10
Purchase #4	$246.72	13.103%	$279.0477	$279.05	$279.05	$279.00
Purchase #5	$186.47	12.412%	$209.6147	$209.61	$209.60	$209.60
Purchase #6	$89.65	11.272%	$99.7553	$99.76	$99.75	$99.80
Purchase #7	$62.26	8.165%	$67.3435	$67.34	$67.35	$67.30
7 purchase totals =	$888.05		$982.5505	$982.55	$982.55	$982.40