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	$73.67	7.865%	$79.4641	$79.46	$79.45	$79.50
Purchase #2	$247.40	12.563%	$278.4809	$278.48	$278.50	$278.50
Purchase #3	$181.80	4.797%	$190.5209	$190.52	$190.50	$190.50
Purchase #4	$171.90	3.768%	$178.3772	$178.38	$178.40	$178.40
Purchase #5	$79.36	9.491%	$86.8921	$86.89	$86.90	$86.90
Purchase #6	$156.62	12.311%	$175.9015	$175.90	$175.90	$175.90
Purchase #7	$151.49	12.563%	$170.5217	$170.52	$170.50	$170.50
7 purchase totals =	$1,062.24		$1,160.1584	$1,160.15	$1,160.15	$1,160.20