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	$42.43	3.229%	$43.8001	$43.80	$43.80	$43.80
Purchase #2	$37.67	12.189%	$42.2616	$42.26	$42.25	$42.30
Purchase #3	$196.35	13.351%	$222.5647	$222.56	$222.55	$222.60
Purchase #4	$35.36	9.664%	$38.7772	$38.78	$38.80	$38.80
Purchase #5	$72.88	10.780%	$80.7365	$80.74	$80.75	$80.70
Purchase #6	$169.38	4.368%	$176.7785	$176.78	$176.80	$176.80
Purchase #7	$53.40	11.808%	$59.7055	$59.71	$59.70	$59.70
7 purchase totals =	$607.47		$664.6241	$664.63	$664.65	$664.70