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	$55.47	9.858%	$60.9382	$60.94	$60.95	$60.90
Purchase #2	$168.30	6.631%	$179.46	$179.46	$179.45	$179.50
Purchase #3	$107.82	4.391%	$112.5544	$112.55	$112.55	$112.60
Purchase #4	$103.51	8.630%	$112.4429	$112.44	$112.45	$112.40
Purchase #5	$93.34	10.145%	$102.8093	$102.81	$102.80	$102.80
Purchase #6	$208.55	11.190%	$231.8867	$231.89	$231.90	$231.90
Purchase #7	$50.41	10.872%	$55.8906	$55.89	$55.90	$55.90
7 purchase totals =	$787.40		$855.9821	$855.98	$856.00	$856.00