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	$76.48	8.668%	$83.1093	$83.11	$83.10	$83.10
Purchase #2	$208.46	4.336%	$217.4988	$217.50	$217.50	$217.50
Purchase #3	$90.51	9.601%	$99.1999	$99.20	$99.20	$99.20
Purchase #4	$134.73	5.707%	$142.419	$142.42	$142.40	$142.40
Purchase #5	$245.95	13.439%	$279.0032	$279.00	$279.00	$279.00
Purchase #6	$133.88	5.441%	$141.1644	$141.16	$141.15	$141.20
Purchase #7	$14.31	8.697%	$15.5545	$15.55	$15.55	$15.60
7 purchase totals =	$904.32		$977.9491	$977.94	$977.90	$978.00