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	$107.30	3.646%	$111.2122	$111.21	$111.20	$111.20
Purchase #2	$76.80	7.204%	$82.3327	$82.33	$82.35	$82.30
Purchase #3	$18.94	9.166%	$20.676	$20.68	$20.70	$20.70
Purchase #4	$164.86	11.250%	$183.4068	$183.41	$183.40	$183.40
Purchase #5	$76.93	8.157%	$83.2052	$83.21	$83.20	$83.20
Purchase #6	$248.88	5.346%	$262.1851	$262.19	$262.20	$262.20
Purchase #7	$85.50	5.435%	$90.1469	$90.15	$90.15	$90.10
7 purchase totals =	$779.21		$833.1649	$833.18	$833.20	$833.10