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	$145.36	3.822%	$150.9157	$150.92	$150.90	$150.90
Purchase #2	$168.32	13.108%	$190.3834	$190.38	$190.40	$190.40
Purchase #3	$142.31	6.151%	$151.0635	$151.06	$151.05	$151.10
Purchase #4	$249.57	11.380%	$277.9711	$277.97	$277.95	$278.00
Purchase #5	$55.68	12.611%	$62.7018	$62.70	$62.70	$62.70
Purchase #6	$237.35	10.704%	$262.7559	$262.76	$262.75	$262.80
Purchase #7	$150.78	11.442%	$168.0322	$168.03	$168.05	$168.00
7 purchase totals =	$1,149.37		$1,263.8236	$1,263.82	$1,263.80	$1,263.90