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	$30.25	7.574%	$32.5411	$32.54	$32.55	$32.50
Purchase #2	$59.68	12.868%	$67.3596	$67.36	$67.35	$67.40
Purchase #3	$182.82	12.161%	$205.0527	$205.05	$205.05	$205.10
Purchase #4	$82.66	13.771%	$94.0431	$94.04	$94.05	$94.00
Purchase #5	$41.56	3.171%	$42.8779	$42.88	$42.90	$42.90
Purchase #6	$217.60	7.468%	$233.8504	$233.85	$233.85	$233.90
Purchase #7	$144.90	6.328%	$154.0693	$154.07	$154.05	$154.10
7 purchase totals =	$759.47		$829.7941	$829.79	$829.80	$829.90