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	$131.42	7.347%	$141.0754	$141.08	$141.10	$141.10
Purchase #2	$121.36	12.663%	$136.7278	$136.73	$136.75	$136.70
Purchase #3	$168.47	5.852%	$178.3289	$178.33	$178.35	$178.30
Purchase #4	$149.83	10.665%	$165.8094	$165.81	$165.80	$165.80
Purchase #5	$57.31	8.574%	$62.2238	$62.22	$62.20	$62.20
Purchase #6	$225.88	6.636%	$240.8694	$240.87	$240.85	$240.90
Purchase #7	$53.56	11.221%	$59.57	$59.57	$59.55	$59.60
7 purchase totals =	$907.83		$984.6047	$984.61	$984.60	$984.60