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	$34.53	12.425%	$38.8204	$38.82	$38.80	$38.80
Purchase #2	$188.64	9.155%	$205.91	$205.91	$205.90	$205.90
Purchase #3	$20.25	6.618%	$21.5901	$21.59	$21.60	$21.60
Purchase #4	$18.71	10.286%	$20.6345	$20.63	$20.65	$20.60
Purchase #5	$169.93	7.518%	$182.7053	$182.71	$182.70	$182.70
Purchase #6	$250.37	5.284%	$263.5996	$263.60	$263.60	$263.60
Purchase #7	$172.57	10.749%	$191.1195	$191.12	$191.10	$191.10
7 purchase totals =	$855.00		$924.3794	$924.38	$924.35	$924.30