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	$58.46	11.812%	$65.3653	$65.37	$65.35	$65.40
Purchase #2	$75.94	4.583%	$79.4203	$79.42	$79.40	$79.40
Purchase #3	$147.69	12.799%	$166.5928	$166.59	$166.60	$166.60
Purchase #4	$180.95	3.253%	$186.8363	$186.84	$186.85	$186.80
Purchase #5	$58.88	10.542%	$65.0871	$65.09	$65.10	$65.10
Purchase #6	$57.41	12.601%	$64.6442	$64.64	$64.65	$64.60
Purchase #7	$35.28	9.418%	$38.6027	$38.60	$38.60	$38.60
7 purchase totals =	$614.61		$666.5487	$666.55	$666.55	$666.50