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	$39.48	10.109%	$43.471	$43.47	$43.45	$43.50
Purchase #2	$212.42	7.608%	$228.5809	$228.58	$228.60	$228.60
Purchase #3	$35.60	11.837%	$39.814	$39.81	$39.80	$39.80
Purchase #4	$52.30	6.713%	$55.8109	$55.81	$55.80	$55.80
Purchase #5	$170.90	10.637%	$189.0786	$189.08	$189.10	$189.10
Purchase #6	$32.41	8.726%	$35.2381	$35.24	$35.25	$35.20
Purchase #7	$76.46	11.280%	$85.0847	$85.08	$85.10	$85.10
7 purchase totals =	$619.57		$677.0782	$677.07	$677.10	$677.10