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	$33.53	13.184%	$37.9506	$37.95	$37.95	$38.00
Purchase #2	$178.69	5.416%	$188.3679	$188.37	$188.35	$188.40
Purchase #3	$91.84	6.738%	$98.0282	$98.03	$98.05	$98.00
Purchase #4	$90.43	12.602%	$101.826	$101.83	$101.85	$101.80
Purchase #5	$41.36	3.434%	$42.7803	$42.78	$42.80	$42.80
Purchase #6	$147.69	5.593%	$155.9503	$155.95	$155.95	$156.00
Purchase #7	$122.48	6.653%	$130.6286	$130.63	$130.65	$130.60
7 purchase totals =	$706.02		$755.5319	$755.54	$755.60	$755.60