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	$31.63	10.660%	$35.0018	$35.00	$35.00	$35.00
Purchase #2	$52.31	4.666%	$54.7508	$54.75	$54.75	$54.80
Purchase #3	$207.60	5.564%	$219.1509	$219.15	$219.15	$219.20
Purchase #4	$121.61	12.518%	$136.8331	$136.83	$136.85	$136.80
Purchase #5	$134.69	12.387%	$151.3741	$151.37	$151.35	$151.40
Purchase #6	$150.45	7.756%	$162.1189	$162.12	$162.10	$162.10
Purchase #7	$75.67	3.464%	$78.2912	$78.29	$78.30	$78.30
7 purchase totals =	$773.96		$837.5208	$837.51	$837.50	$837.60