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	$141.72	6.197%	$150.5024	$150.50	$150.50	$150.50
Purchase #2	$243.67	4.601%	$254.8813	$254.88	$254.90	$254.90
Purchase #3	$107.82	4.750%	$112.9415	$112.94	$112.95	$112.90
Purchase #4	$202.66	11.790%	$226.5536	$226.55	$226.55	$226.60
Purchase #5	$215.46	7.142%	$230.8482	$230.85	$230.85	$230.80
Purchase #6	$36.85	10.660%	$40.7782	$40.78	$40.80	$40.80
Purchase #7	$22.82	5.275%	$24.0238	$24.02	$24.00	$24.00
7 purchase totals =	$971.00		$1,040.5290	$1,040.52	$1,040.55	$1,040.50