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	$119.61	10.226%	$131.8413	$131.84	$131.85	$131.80
Purchase #2	$87.39	3.436%	$90.3927	$90.39	$90.40	$90.40
Purchase #3	$178.51	6.230%	$189.6312	$189.63	$189.65	$189.60
Purchase #4	$208.41	12.382%	$234.2153	$234.22	$234.20	$234.20
Purchase #5	$79.27	7.414%	$85.1471	$85.15	$85.15	$85.10
Purchase #6	$18.28	10.524%	$20.2038	$20.20	$20.20	$20.20
Purchase #7	$10.36	7.857%	$11.174	$11.17	$11.15	$11.20
7 purchase totals =	$701.83		$762.6054	$762.60	$762.60	$762.50