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	$49.79	3.444%	$51.5048	$51.50	$51.50	$51.50
Purchase #2	$201.79	3.743%	$209.343	$209.34	$209.35	$209.30
Purchase #3	$198.77	12.309%	$223.2366	$223.24	$223.25	$223.20
Purchase #4	$9.79	3.754%	$10.1575	$10.16	$10.15	$10.20
Purchase #5	$134.94	5.601%	$142.498	$142.50	$142.50	$142.50
Purchase #6	$33.55	12.866%	$37.8665	$37.87	$37.85	$37.90
Purchase #7	$214.31	12.427%	$240.9423	$240.94	$240.95	$240.90
7 purchase totals =	$842.94		$915.5487	$915.55	$915.55	$915.50