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	$104.95	4.357%	$109.5227	$109.52	$109.50	$109.50
Purchase #2	$82.65	7.288%	$88.6735	$88.67	$88.65	$88.70
Purchase #3	$169.59	12.836%	$191.3586	$191.36	$191.35	$191.40
Purchase #4	$18.40	3.671%	$19.0755	$19.08	$19.10	$19.10
Purchase #5	$244.79	4.506%	$255.8202	$255.82	$255.80	$255.80
Purchase #6	$44.95	6.820%	$48.0156	$48.02	$48.00	$48.00
Purchase #7	$244.33	12.103%	$273.9013	$273.90	$273.90	$273.90
7 purchase totals =	$909.66		$986.3674	$986.37	$986.30	$986.40