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	$74.30	5.667%	$78.5106	$78.51	$78.50	$78.50
Purchase #2	$155.79	13.327%	$176.5521	$176.55	$176.55	$176.60
Purchase #3	$65.47	13.523%	$74.3235	$74.32	$74.30	$74.30
Purchase #4	$168.72	4.674%	$176.606	$176.61	$176.60	$176.60
Purchase #5	$118.59	6.426%	$126.2106	$126.21	$126.20	$126.20
Purchase #6	$190.30	13.810%	$216.5804	$216.58	$216.60	$216.60
Purchase #7	$11.56	9.425%	$12.6495	$12.65	$12.65	$12.60
7 purchase totals =	$784.73		$861.4327	$861.43	$861.40	$861.40