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	$78.33	8.693%	$85.1392	$85.14	$85.15	$85.10
Purchase #2	$128.38	8.705%	$139.5555	$139.56	$139.55	$139.60
Purchase #3	$131.63	3.701%	$136.5016	$136.50	$136.50	$136.50
Purchase #4	$119.52	12.425%	$134.3704	$134.37	$134.35	$134.40
Purchase #5	$58.38	3.792%	$60.5938	$60.59	$60.60	$60.60
Purchase #6	$47.73	10.655%	$52.8156	$52.82	$52.80	$52.80
Purchase #7	$213.61	13.110%	$241.6143	$241.61	$241.60	$241.60
7 purchase totals =	$777.58		$850.5904	$850.59	$850.55	$850.60