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	$139.80	8.807%	$152.1122	$152.11	$152.10	$152.10
Purchase #2	$36.59	11.557%	$40.8187	$40.82	$40.80	$40.80
Purchase #3	$160.43	3.108%	$165.4162	$165.42	$165.40	$165.40
Purchase #4	$123.42	12.767%	$139.177	$139.18	$139.20	$139.20
Purchase #5	$213.30	12.199%	$239.3205	$239.32	$239.30	$239.30
Purchase #6	$149.47	3.606%	$154.8599	$154.86	$154.85	$154.90
Purchase #7	$18.99	13.105%	$21.4786	$21.48	$21.50	$21.50
7 purchase totals =	$842.00		$913.1831	$913.19	$913.15	$913.20