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	$202.51	4.297%	$211.2119	$211.21	$211.20	$211.20
Purchase #2	$183.33	7.340%	$196.7864	$196.79	$196.80	$196.80
Purchase #3	$150.54	11.725%	$168.1908	$168.19	$168.20	$168.20
Purchase #4	$134.47	5.235%	$141.5095	$141.51	$141.50	$141.50
Purchase #5	$233.31	10.628%	$258.1062	$258.11	$258.10	$258.10
Purchase #6	$192.86	13.748%	$219.3744	$219.37	$219.35	$219.40
Purchase #7	$127.33	11.478%	$141.9449	$141.94	$141.95	$141.90
7 purchase totals =	$1,224.35		$1,337.1241	$1,337.12	$1,337.10	$1,337.10