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	$103.62	12.801%	$116.8844	$116.88	$116.90	$116.90
Purchase #2	$218.87	4.861%	$229.5093	$229.51	$229.50	$229.50
Purchase #3	$92.38	10.666%	$102.2333	$102.23	$102.25	$102.20
Purchase #4	$133.38	4.365%	$139.202	$139.20	$139.20	$139.20
Purchase #5	$179.98	9.233%	$196.5976	$196.60	$196.60	$196.60
Purchase #6	$198.96	10.109%	$219.0729	$219.07	$219.05	$219.10
Purchase #7	$100.68	7.385%	$108.1152	$108.12	$108.10	$108.10
7 purchase totals =	$1,027.87		$1,111.6147	$1,111.61	$1,111.60	$1,111.60