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	$221.37	7.306%	$237.5433	$237.54	$237.55	$237.50
Purchase #2	$202.51	13.704%	$230.262	$230.26	$230.25	$230.30
Purchase #3	$42.58	12.449%	$47.8808	$47.88	$47.90	$47.90
Purchase #4	$93.92	11.732%	$104.9387	$104.94	$104.95	$104.90
Purchase #5	$168.72	13.206%	$191.0012	$191.00	$191.00	$191.00
Purchase #6	$40.40	6.129%	$42.8761	$42.88	$42.90	$42.90
Purchase #7	$245.88	13.218%	$278.3804	$278.38	$278.40	$278.40
7 purchase totals =	$1,015.38		$1,132.8825	$1,132.88	$1,132.95	$1,132.90