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	$34.61	8.213%	$37.4525	$37.45	$37.45	$37.50
Purchase #2	$52.61	8.511%	$57.0876	$57.09	$57.10	$57.10
Purchase #3	$168.97	10.576%	$186.8403	$186.84	$186.85	$186.80
Purchase #4	$163.40	4.807%	$171.2546	$171.25	$171.25	$171.30
Purchase #5	$130.39	6.355%	$138.6763	$138.68	$138.70	$138.70
Purchase #6	$78.72	13.814%	$89.5944	$89.59	$89.60	$89.60
Purchase #7	$159.42	7.142%	$170.8058	$170.81	$170.80	$170.80
7 purchase totals =	$788.12		$851.7115	$851.71	$851.75	$851.80