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	$91.27	8.722%	$99.2306	$99.23	$99.25	$99.20
Purchase #2	$168.49	9.514%	$184.5201	$184.52	$184.50	$184.50
Purchase #3	$17.99	4.631%	$18.8231	$18.82	$18.80	$18.80
Purchase #4	$43.67	6.641%	$46.5701	$46.57	$46.55	$46.60
Purchase #5	$72.66	12.729%	$81.9089	$81.91	$81.90	$81.90
Purchase #6	$58.78	13.615%	$66.7829	$66.78	$66.80	$66.80
Purchase #7	$126.92	12.591%	$142.9005	$142.90	$142.90	$142.90
7 purchase totals =	$579.78		$640.7362	$640.73	$640.70	$640.70