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	$36.78	12.634%	$41.4268	$41.43	$41.45	$41.40
Purchase #2	$205.86	12.570%	$231.7366	$231.74	$231.75	$231.70
Purchase #3	$142.30	13.498%	$161.5077	$161.51	$161.50	$161.50
Purchase #4	$168.25	4.521%	$175.8566	$175.86	$175.85	$175.90
Purchase #5	$145.71	7.402%	$156.4955	$156.50	$156.50	$156.50
Purchase #6	$90.56	8.649%	$98.3925	$98.39	$98.40	$98.40
Purchase #7	$19.68	5.780%	$20.8175	$20.82	$20.80	$20.80
7 purchase totals =	$809.14		$886.2332	$886.25	$886.25	$886.20