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	$129.95	9.533%	$142.3381	$142.34	$142.35	$142.30
Purchase #2	$107.26	10.490%	$118.5116	$118.51	$118.50	$118.50
Purchase #3	$141.81	7.849%	$152.9407	$152.94	$152.95	$152.90
Purchase #4	$72.81	12.558%	$81.9535	$81.95	$81.95	$82.00
Purchase #5	$17.79	13.294%	$20.155	$20.16	$20.15	$20.20
Purchase #6	$191.87	13.787%	$218.3231	$218.32	$218.30	$218.30
Purchase #7	$114.96	7.177%	$123.2107	$123.21	$123.20	$123.20
7 purchase totals =	$776.45		$857.4327	$857.43	$857.40	$857.40