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	$154.34	6.779%	$164.8027	$164.80	$164.80	$164.80
Purchase #2	$60.33	12.638%	$67.9545	$67.95	$67.95	$68.00
Purchase #3	$191.47	13.273%	$216.8838	$216.88	$216.90	$216.90
Purchase #4	$208.44	12.234%	$233.9405	$233.94	$233.95	$233.90
Purchase #5	$44.38	4.686%	$46.4596	$46.46	$46.45	$46.50
Purchase #6	$67.71	4.139%	$70.5125	$70.51	$70.50	$70.50
Purchase #7	$91.27	9.111%	$99.5856	$99.59	$99.60	$99.60
7 purchase totals =	$817.94		$900.1392	$900.13	$900.15	$900.20