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	$139.52	12.562%	$157.0465	$157.05	$157.05	$157.00
Purchase #2	$159.33	12.578%	$179.3705	$179.37	$179.35	$179.40
Purchase #3	$248.83	7.242%	$266.8503	$266.85	$266.85	$266.90
Purchase #4	$164.57	13.692%	$187.1029	$187.10	$187.10	$187.10
Purchase #5	$6.39	13.535%	$7.2549	$7.25	$7.25	$7.30
Purchase #6	$17.62	3.400%	$18.2191	$18.22	$18.20	$18.20
Purchase #7	$250.87	11.810%	$280.4977	$280.50	$280.50	$280.50
7 purchase totals =	$987.13		$1,096.3419	$1,096.34	$1,096.30	$1,096.40