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	$130.34	5.698%	$137.7668	$137.77	$137.75	$137.80
Purchase #2	$36.33	11.777%	$40.6086	$40.61	$40.60	$40.60
Purchase #3	$98.62	10.557%	$109.0313	$109.03	$109.05	$109.00
Purchase #4	$58.25	13.691%	$66.225	$66.23	$66.25	$66.20
Purchase #5	$186.86	4.287%	$194.8707	$194.87	$194.85	$194.90
Purchase #6	$146.63	12.116%	$164.3957	$164.40	$164.40	$164.40
Purchase #7	$235.32	3.408%	$243.3397	$243.34	$243.35	$243.30
7 purchase totals =	$892.35		$956.2378	$956.25	$956.25	$956.20