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	$227.51	5.664%	$240.3962	$240.40	$240.40	$240.40
Purchase #2	$41.33	10.291%	$45.5833	$45.58	$45.60	$45.60
Purchase #3	$41.66	11.626%	$46.5034	$46.50	$46.50	$46.50
Purchase #4	$39.56	10.706%	$43.7953	$43.80	$43.80	$43.80
Purchase #5	$63.97	6.503%	$68.13	$68.13	$68.15	$68.10
Purchase #6	$245.70	12.395%	$276.1545	$276.15	$276.15	$276.20
Purchase #7	$55.71	7.346%	$59.8025	$59.80	$59.80	$59.80
7 purchase totals =	$715.44		$780.3652	$780.36	$780.40	$780.40