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	$32.92	12.845%	$37.1486	$37.15	$37.15	$37.10
Purchase #2	$210.30	13.216%	$238.0932	$238.09	$238.10	$238.10
Purchase #3	$123.67	13.225%	$140.0254	$140.03	$140.05	$140.00
Purchase #4	$170.90	12.505%	$192.271	$192.27	$192.25	$192.30
Purchase #5	$168.52	8.529%	$182.8931	$182.89	$182.90	$182.90
Purchase #6	$72.34	9.388%	$79.1313	$79.13	$79.15	$79.10
Purchase #7	$86.50	4.272%	$90.1953	$90.20	$90.20	$90.20
7 purchase totals =	$865.15		$959.7579	$959.76	$959.80	$959.70