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	$60.54	10.852%	$67.1098	$67.11	$67.10	$67.10
Purchase #2	$141.49	4.267%	$147.5274	$147.53	$147.55	$147.50
Purchase #3	$168.50	13.257%	$190.838	$190.84	$190.85	$190.80
Purchase #4	$29.64	6.233%	$31.4875	$31.49	$31.50	$31.50
Purchase #5	$65.42	11.397%	$72.8759	$72.88	$72.90	$72.90
Purchase #6	$82.85	8.782%	$90.1259	$90.13	$90.15	$90.10
Purchase #7	$51.46	13.158%	$58.2311	$58.23	$58.25	$58.20
7 purchase totals =	$599.90		$658.1956	$658.21	$658.30	$658.10