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	$91.56	10.126%	$100.8314	$100.83	$100.85	$100.80
Purchase #2	$50.36	10.756%	$55.7767	$55.78	$55.80	$55.80
Purchase #3	$103.70	12.665%	$116.8336	$116.83	$116.85	$116.80
Purchase #4	$62.55	10.717%	$69.2535	$69.25	$69.25	$69.30
Purchase #5	$151.93	10.726%	$168.226	$168.23	$168.25	$168.20
Purchase #6	$247.34	12.663%	$278.6607	$278.66	$278.65	$278.70
Purchase #7	$69.29	10.560%	$76.607	$76.61	$76.60	$76.60
7 purchase totals =	$776.73		$866.1889	$866.19	$866.25	$866.20