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	$35.69	13.447%	$40.4892	$40.49	$40.50	$40.50
Purchase #2	$135.29	5.295%	$142.4536	$142.45	$142.45	$142.50
Purchase #3	$88.47	6.139%	$93.9012	$93.90	$93.90	$93.90
Purchase #4	$183.29	5.602%	$193.5579	$193.56	$193.55	$193.60
Purchase #5	$191.38	12.772%	$215.8231	$215.82	$215.80	$215.80
Purchase #6	$91.81	9.862%	$100.8643	$100.86	$100.85	$100.90
Purchase #7	$246.54	13.116%	$278.8762	$278.88	$278.90	$278.90
7 purchase totals =	$972.47		$1,065.9655	$1,065.96	$1,065.95	$1,066.10