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	$19.40	7.764%	$20.9062	$20.91	$20.90	$20.90
Purchase #2	$83.70	12.854%	$94.4588	$94.46	$94.45	$94.50
Purchase #3	$40.78	4.169%	$42.4801	$42.48	$42.50	$42.50
Purchase #4	$33.75	10.140%	$37.1723	$37.17	$37.15	$37.20
Purchase #5	$176.30	7.110%	$188.8349	$188.83	$188.85	$188.80
Purchase #6	$192.75	6.297%	$204.8875	$204.89	$204.90	$204.90
Purchase #7	$78.30	3.754%	$81.2394	$81.24	$81.25	$81.20
7 purchase totals =	$624.98		$669.9792	$669.98	$670.00	$670.00