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	$35.78	8.704%	$38.8943	$38.89	$38.90	$38.90
Purchase #2	$219.46	6.618%	$233.9839	$233.98	$234.00	$234.00
Purchase #3	$25.29	6.631%	$26.967	$26.97	$26.95	$27.00
Purchase #4	$100.71	8.747%	$109.5191	$109.52	$109.50	$109.50
Purchase #5	$167.72	10.250%	$184.9113	$184.91	$184.90	$184.90
Purchase #6	$22.94	5.333%	$24.1634	$24.16	$24.15	$24.20
Purchase #7	$208.46	6.620%	$222.2601	$222.26	$222.25	$222.30
7 purchase totals =	$780.36		$840.6991	$840.69	$840.65	$840.80