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	$5.88	3.428%	$6.0816	$6.08	$6.10	$6.10
Purchase #2	$190.74	4.561%	$199.4397	$199.44	$199.45	$199.40
Purchase #3	$156.67	10.245%	$172.7208	$172.72	$172.70	$172.70
Purchase #4	$13.96	13.202%	$15.803	$15.80	$15.80	$15.80
Purchase #5	$39.91	13.162%	$45.163	$45.16	$45.15	$45.20
Purchase #6	$156.67	10.305%	$172.8148	$172.81	$172.80	$172.80
Purchase #7	$136.92	8.770%	$148.9279	$148.93	$148.95	$148.90
7 purchase totals =	$700.75		$760.9508	$760.94	$760.95	$760.90