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	$94.34	6.535%	$100.5051	$100.51	$100.50	$100.50
Purchase #2	$99.61	5.299%	$104.8883	$104.89	$104.90	$104.90
Purchase #3	$59.81	13.479%	$67.8718	$67.87	$67.85	$67.90
Purchase #4	$125.37	4.363%	$130.8399	$130.84	$130.85	$130.80
Purchase #5	$87.28	7.320%	$93.6689	$93.67	$93.65	$93.70
Purchase #6	$239.63	12.434%	$269.4256	$269.43	$269.45	$269.40
Purchase #7	$117.86	11.672%	$131.6166	$131.62	$131.60	$131.60
7 purchase totals =	$823.90		$898.8162	$898.83	$898.80	$898.80