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	$248.33	3.412%	$256.803	$256.80	$256.80	$256.80
Purchase #2	$38.26	9.364%	$41.8427	$41.84	$41.85	$41.80
Purchase #3	$123.64	9.604%	$135.5144	$135.51	$135.50	$135.50
Purchase #4	$240.61	13.811%	$273.8406	$273.84	$273.85	$273.80
Purchase #5	$64.93	4.126%	$67.609	$67.61	$67.60	$67.60
Purchase #6	$85.58	8.598%	$92.9382	$92.94	$92.95	$92.90
Purchase #7	$124.50	5.685%	$131.5778	$131.58	$131.60	$131.60
7 purchase totals =	$925.85		$1,000.1257	$1,000.12	$1,000.15	$1,000.00