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	$53.41	6.333%	$56.7925	$56.79	$56.80	$56.80
Purchase #2	$172.49	13.383%	$195.5743	$195.57	$195.55	$195.60
Purchase #3	$171.54	6.346%	$182.4259	$182.43	$182.45	$182.40
Purchase #4	$135.60	12.505%	$152.5568	$152.56	$152.55	$152.60
Purchase #5	$10.88	8.485%	$11.8032	$11.80	$11.80	$11.80
Purchase #6	$78.60	3.815%	$81.5986	$81.60	$81.60	$81.60
Purchase #7	$69.43	12.432%	$78.0615	$78.06	$78.05	$78.10
7 purchase totals =	$691.95		$758.8128	$758.81	$758.80	$758.90