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	$33.75	12.438%	$37.9478	$37.95	$37.95	$37.90
Purchase #2	$74.68	11.859%	$83.5363	$83.54	$83.55	$83.50
Purchase #3	$240.82	8.433%	$261.1284	$261.13	$261.15	$261.10
Purchase #4	$50.64	3.189%	$52.2549	$52.25	$52.25	$52.30
Purchase #5	$180.56	8.731%	$196.3247	$196.32	$196.30	$196.30
Purchase #6	$145.61	5.692%	$153.8981	$153.90	$153.90	$153.90
Purchase #7	$230.88	12.701%	$260.2041	$260.20	$260.20	$260.20
7 purchase totals =	$956.94		$1,045.2943	$1,045.29	$1,045.30	$1,045.20