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	$17.57	8.741%	$19.1058	$19.11	$19.10	$19.10
Purchase #2	$19.96	7.398%	$21.4366	$21.44	$21.45	$21.40
Purchase #3	$76.61	7.322%	$82.2194	$82.22	$82.20	$82.20
Purchase #4	$136.66	10.340%	$150.7906	$150.79	$150.80	$150.80
Purchase #5	$184.44	8.592%	$200.2871	$200.29	$200.30	$200.30
Purchase #6	$57.39	11.329%	$63.8917	$63.89	$63.90	$63.90
Purchase #7	$41.73	4.602%	$43.6504	$43.65	$43.65	$43.70
7 purchase totals =	$534.36		$581.3816	$581.39	$581.40	$581.40