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	$219.89	6.106%	$233.3165	$233.32	$233.30	$233.30
Purchase #2	$94.74	9.271%	$103.5233	$103.52	$103.50	$103.50
Purchase #3	$41.66	6.222%	$44.2521	$44.25	$44.25	$44.30
Purchase #4	$233.89	13.538%	$265.554	$265.55	$265.55	$265.60
Purchase #5	$155.32	8.784%	$168.9633	$168.96	$168.95	$169.00
Purchase #6	$39.96	9.631%	$43.8085	$43.81	$43.80	$43.80
Purchase #7	$85.59	12.138%	$95.9789	$95.98	$96.00	$96.00
7 purchase totals =	$871.05		$955.3966	$955.39	$955.35	$955.50