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	$45.59	12.633%	$51.3494	$51.35	$51.35	$51.30
Purchase #2	$115.32	7.293%	$123.7303	$123.73	$123.75	$123.70
Purchase #3	$139.32	8.629%	$151.3419	$151.34	$151.35	$151.30
Purchase #4	$26.86	12.346%	$30.1761	$30.18	$30.20	$30.20
Purchase #5	$84.60	4.717%	$88.5906	$88.59	$88.60	$88.60
Purchase #6	$104.53	4.337%	$109.0635	$109.06	$109.05	$109.10
Purchase #7	$61.92	5.458%	$65.2996	$65.30	$65.30	$65.30
7 purchase totals =	$578.14		$619.5514	$619.55	$619.60	$619.50