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	$11.30	12.838%	$12.7507	$12.75	$12.75	$12.80
Purchase #2	$113.68	12.718%	$128.1378	$128.14	$128.15	$128.10
Purchase #3	$47.86	10.424%	$52.8489	$52.85	$52.85	$52.80
Purchase #4	$29.54	11.444%	$32.9206	$32.92	$32.90	$32.90
Purchase #5	$131.82	4.437%	$137.6689	$137.67	$137.65	$137.70
Purchase #6	$194.34	4.746%	$203.5634	$203.56	$203.55	$203.60
Purchase #7	$188.78	6.200%	$200.4844	$200.48	$200.50	$200.50
7 purchase totals =	$717.32		$768.3747	$768.37	$768.35	$768.40