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	$80.57	3.683%	$83.5374	$83.54	$83.55	$83.50
Purchase #2	$128.52	6.439%	$136.7954	$136.80	$136.80	$136.80
Purchase #3	$60.51	6.873%	$64.6689	$64.67	$64.65	$64.70
Purchase #4	$110.81	7.784%	$119.4355	$119.44	$119.45	$119.40
Purchase #5	$103.38	6.181%	$109.7699	$109.77	$109.75	$109.80
Purchase #6	$95.53	5.368%	$100.6581	$100.66	$100.65	$100.70
Purchase #7	$131.86	11.446%	$146.9527	$146.95	$146.95	$147.00
7 purchase totals =	$711.18		$761.8179	$761.83	$761.80	$761.90