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	$7.31	6.435%	$7.7804	$7.78	$7.80	$7.80
Purchase #2	$215.58	10.594%	$238.4185	$238.42	$238.40	$238.40
Purchase #3	$150.32	6.171%	$159.5962	$159.60	$159.60	$159.60
Purchase #4	$123.83	6.181%	$131.4839	$131.48	$131.50	$131.50
Purchase #5	$155.92	6.755%	$166.4524	$166.45	$166.45	$166.50
Purchase #6	$173.41	7.673%	$186.7157	$186.72	$186.70	$186.70
Purchase #7	$185.63	7.182%	$198.9619	$198.96	$198.95	$199.00
7 purchase totals =	$1,012.00		$1,089.4090	$1,089.41	$1,089.40	$1,089.50