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	$234.61	10.307%	$258.7913	$258.79	$258.80	$258.80
Purchase #2	$109.84	4.585%	$114.8762	$114.88	$114.90	$114.90
Purchase #3	$150.81	5.358%	$158.8904	$158.89	$158.90	$158.90
Purchase #4	$232.94	11.359%	$259.3997	$259.40	$259.40	$259.40
Purchase #5	$30.99	7.594%	$33.3434	$33.34	$33.35	$33.30
Purchase #6	$190.99	13.404%	$216.5903	$216.59	$216.60	$216.60
Purchase #7	$91.42	10.304%	$100.8399	$100.84	$100.85	$100.80
7 purchase totals =	$1,041.60		$1,142.7312	$1,142.73	$1,142.80	$1,142.70