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	$123.55	4.231%	$128.7774	$128.78	$128.80	$128.80
Purchase #2	$66.85	3.573%	$69.2386	$69.24	$69.25	$69.20
Purchase #3	$120.47	9.166%	$131.5123	$131.51	$131.50	$131.50
Purchase #4	$93.83	8.125%	$101.4537	$101.45	$101.45	$101.50
Purchase #5	$103.74	11.158%	$115.3153	$115.32	$115.30	$115.30
Purchase #6	$85.66	5.323%	$90.2197	$90.22	$90.20	$90.20
Purchase #7	$174.63	7.665%	$188.0154	$188.02	$188.00	$188.00
7 purchase totals =	$768.73		$824.5324	$824.54	$824.50	$824.50