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	$32.33	7.353%	$34.7072	$34.71	$34.70	$34.70
Purchase #2	$223.39	12.419%	$251.1328	$251.13	$251.15	$251.10
Purchase #3	$33.44	8.186%	$36.1774	$36.18	$36.20	$36.20
Purchase #4	$84.36	6.479%	$89.8257	$89.83	$89.85	$89.80
Purchase #5	$137.52	7.866%	$148.3373	$148.34	$148.35	$148.30
Purchase #6	$87.95	13.115%	$99.4846	$99.48	$99.50	$99.50
Purchase #7	$103.73	5.856%	$109.8044	$109.80	$109.80	$109.80
7 purchase totals =	$702.72		$769.4694	$769.47	$769.55	$769.40