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	$102.45	13.519%	$116.3002	$116.30	$116.30	$116.30
Purchase #2	$185.60	8.186%	$200.7932	$200.79	$200.80	$200.80
Purchase #3	$187.30	5.131%	$196.9104	$196.91	$196.90	$196.90
Purchase #4	$111.83	12.517%	$125.8278	$125.83	$125.85	$125.80
Purchase #5	$150.53	13.743%	$171.2173	$171.22	$171.20	$171.20
Purchase #6	$135.77	7.459%	$145.8971	$145.90	$145.90	$145.90
Purchase #7	$222.98	8.805%	$242.6134	$242.61	$242.60	$242.60
7 purchase totals =	$1,096.46		$1,199.5594	$1,199.56	$1,199.55	$1,199.50