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	$129.73	7.244%	$139.1276	$139.13	$139.15	$139.10
Purchase #2	$224.67	3.504%	$232.5424	$232.54	$232.55	$232.50
Purchase #3	$37.65	13.700%	$42.8081	$42.81	$42.80	$42.80
Purchase #4	$113.87	10.674%	$126.0245	$126.02	$126.00	$126.00
Purchase #5	$162.69	3.795%	$168.8641	$168.86	$168.85	$168.90
Purchase #6	$64.32	13.530%	$73.0225	$73.02	$73.00	$73.00
Purchase #7	$100.63	11.646%	$112.3494	$112.35	$112.35	$112.30
7 purchase totals =	$833.56		$894.7386	$894.73	$894.70	$894.60