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	$150.28	12.355%	$168.8471	$168.85	$168.85	$168.80
Purchase #2	$94.90	9.452%	$103.8699	$103.87	$103.85	$103.90
Purchase #3	$153.56	12.383%	$172.5753	$172.58	$172.60	$172.60
Purchase #4	$6.78	3.616%	$7.0252	$7.03	$7.05	$7.00
Purchase #5	$96.90	12.459%	$108.9728	$108.97	$108.95	$109.00
Purchase #6	$82.26	4.380%	$85.863	$85.86	$85.85	$85.90
Purchase #7	$130.57	5.223%	$137.3897	$137.39	$137.40	$137.40
7 purchase totals =	$715.25		$784.5430	$784.55	$784.55	$784.60