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	$108.78	3.841%	$112.9582	$112.96	$112.95	$113.00
Purchase #2	$242.60	13.718%	$275.8799	$275.88	$275.90	$275.90
Purchase #3	$113.57	13.347%	$128.7282	$128.73	$128.75	$128.70
Purchase #4	$13.63	13.219%	$15.4317	$15.43	$15.45	$15.40
Purchase #5	$175.90	11.312%	$195.7978	$195.80	$195.80	$195.80
Purchase #6	$29.97	5.720%	$31.6843	$31.68	$31.70	$31.70
Purchase #7	$106.60	4.506%	$111.4034	$111.40	$111.40	$111.40
7 purchase totals =	$791.05		$871.8835	$871.88	$871.95	$871.90