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	$35.53	3.105%	$36.6332	$36.63	$36.65	$36.60
Purchase #2	$44.51	10.353%	$49.1181	$49.12	$49.10	$49.10
Purchase #3	$172.41	4.499%	$180.1667	$180.17	$180.15	$180.20
Purchase #4	$41.44	5.654%	$43.783	$43.78	$43.80	$43.80
Purchase #5	$186.46	7.695%	$200.8081	$200.81	$200.80	$200.80
Purchase #6	$140.30	7.364%	$150.6317	$150.63	$150.65	$150.60
Purchase #7	$227.78	11.674%	$254.371	$254.37	$254.35	$254.40
7 purchase totals =	$848.43		$915.5118	$915.51	$915.50	$915.50