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	$97.98	7.566%	$105.3932	$105.39	$105.40	$105.40
Purchase #2	$53.36	4.678%	$55.8562	$55.86	$55.85	$55.90
Purchase #3	$201.74	12.233%	$226.4189	$226.42	$226.40	$226.40
Purchase #4	$95.71	4.166%	$99.6973	$99.70	$99.70	$99.70
Purchase #5	$61.85	13.561%	$70.2375	$70.24	$70.25	$70.20
Purchase #6	$76.51	7.753%	$82.4418	$82.44	$82.45	$82.40
Purchase #7	$132.99	5.528%	$140.3417	$140.34	$140.35	$140.30
7 purchase totals =	$720.14		$780.3866	$780.39	$780.40	$780.30