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	$52.61	7.184%	$56.3895	$56.39	$56.40	$56.40
Purchase #2	$144.33	5.113%	$151.7096	$151.71	$151.70	$151.70
Purchase #3	$96.88	12.744%	$109.2264	$109.23	$109.25	$109.20
Purchase #4	$127.91	10.593%	$141.4595	$141.46	$141.45	$141.50
Purchase #5	$131.92	5.225%	$138.8128	$138.81	$138.80	$138.80
Purchase #6	$249.45	12.724%	$281.19	$281.19	$281.20	$281.20
Purchase #7	$175.78	10.591%	$194.3969	$194.40	$194.40	$194.40
7 purchase totals =	$978.88		$1,073.1847	$1,073.19	$1,073.20	$1,073.20