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	$40.61	8.121%	$43.9079	$43.91	$43.90	$43.90
Purchase #2	$23.77	4.273%	$24.7857	$24.79	$24.80	$24.80
Purchase #3	$86.95	3.428%	$89.9306	$89.93	$89.95	$89.90
Purchase #4	$56.81	10.591%	$62.8267	$62.83	$62.85	$62.80
Purchase #5	$130.30	12.659%	$146.7947	$146.79	$146.80	$146.80
Purchase #6	$67.25	7.272%	$72.1404	$72.14	$72.15	$72.10
Purchase #7	$19.61	4.376%	$20.4681	$20.47	$20.45	$20.50
7 purchase totals =	$425.30		$460.8541	$460.86	$460.90	$460.80