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	$38.63	9.381%	$42.2539	$42.25	$42.25	$42.30
Purchase #2	$71.32	7.823%	$76.8994	$76.90	$76.90	$76.90
Purchase #3	$175.59	4.267%	$183.0824	$183.08	$183.10	$183.10
Purchase #4	$161.32	12.703%	$181.8125	$181.81	$181.80	$181.80
Purchase #5	$107.46	5.843%	$113.7389	$113.74	$113.75	$113.70
Purchase #6	$136.25	4.111%	$141.8512	$141.85	$141.85	$141.90
Purchase #7	$53.32	8.310%	$57.7509	$57.75	$57.75	$57.80
7 purchase totals =	$743.89		$797.3892	$797.38	$797.40	$797.50