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	$51.93	7.617%	$55.8855	$55.89	$55.90	$55.90
Purchase #2	$145.89	4.732%	$152.7935	$152.79	$152.80	$152.80
Purchase #3	$137.97	3.543%	$142.8583	$142.86	$142.85	$142.90
Purchase #4	$11.75	11.197%	$13.0656	$13.07	$13.05	$13.10
Purchase #5	$136.55	12.507%	$153.6283	$153.63	$153.65	$153.60
Purchase #6	$29.85	5.686%	$31.5473	$31.55	$31.55	$31.50
Purchase #7	$20.57	13.581%	$23.3636	$23.36	$23.35	$23.40
7 purchase totals =	$534.51		$573.1421	$573.15	$573.15	$573.20