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	$135.44	3.271%	$139.8702	$139.87	$139.85	$139.90
Purchase #2	$203.35	7.211%	$218.0136	$218.01	$218.00	$218.00
Purchase #3	$209.89	13.648%	$238.5358	$238.54	$238.55	$238.50
Purchase #4	$9.32	12.339%	$10.47	$10.47	$10.45	$10.50
Purchase #5	$33.61	11.685%	$37.5373	$37.54	$37.55	$37.50
Purchase #6	$44.95	5.244%	$47.3072	$47.31	$47.30	$47.30
Purchase #7	$57.34	6.741%	$61.2053	$61.21	$61.20	$61.20
7 purchase totals =	$693.90		$752.9394	$752.95	$752.90	$752.90