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	12.231%	$105.8787	$105.88	$105.90	$105.90
Purchase #2	$184.48	8.607%	$200.3582	$200.36	$200.35	$200.40
Purchase #3	$83.34	6.587%	$88.8296	$88.83	$88.85	$88.80
Purchase #4	$85.96	3.126%	$88.6471	$88.65	$88.65	$88.60
Purchase #5	$36.30	6.384%	$38.6174	$38.62	$38.60	$38.60
Purchase #6	$95.47	13.611%	$108.4644	$108.46	$108.45	$108.50
Purchase #7	$204.94	8.726%	$222.8231	$222.82	$222.80	$222.80
7 purchase totals =	$784.83		$853.6185	$853.62	$853.60	$853.60