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	$64.92	4.560%	$67.8804	$67.88	$67.90	$67.90
Purchase #2	$145.31	13.392%	$164.7699	$164.77	$164.75	$164.80
Purchase #3	$8.96	13.133%	$10.1367	$10.14	$10.15	$10.10
Purchase #4	$175.72	4.396%	$183.4447	$183.44	$183.45	$183.40
Purchase #5	$217.55	12.417%	$244.5632	$244.56	$244.55	$244.60
Purchase #6	$110.79	11.264%	$123.2694	$123.27	$123.25	$123.30
Purchase #7	$108.74	13.181%	$123.073	$123.07	$123.05	$123.10
7 purchase totals =	$831.99		$917.1373	$917.13	$917.10	$917.20