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	$82.38	9.441%	$90.1575	$90.16	$90.15	$90.20
Purchase #2	$88.93	4.336%	$92.786	$92.79	$92.80	$92.80
Purchase #3	$50.94	10.115%	$56.0926	$56.09	$56.10	$56.10
Purchase #4	$206.96	6.528%	$220.4703	$220.47	$220.45	$220.50
Purchase #5	$29.93	12.799%	$33.7607	$33.76	$33.75	$33.80
Purchase #6	$209.40	11.679%	$233.8558	$233.86	$233.85	$233.90
Purchase #7	$27.54	4.214%	$28.7005	$28.70	$28.70	$28.70
7 purchase totals =	$696.08		$755.8234	$755.83	$755.80	$756.00