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	$34.47	13.638%	$39.171	$39.17	$39.15	$39.20
Purchase #2	$30.35	10.152%	$33.4311	$33.43	$33.45	$33.40
Purchase #3	$164.82	10.831%	$182.6717	$182.67	$182.65	$182.70
Purchase #4	$146.44	11.225%	$162.8779	$162.88	$162.90	$162.90
Purchase #5	$140.96	6.710%	$150.4184	$150.42	$150.40	$150.40
Purchase #6	$240.61	4.413%	$251.2281	$251.23	$251.25	$251.20
Purchase #7	$160.26	12.304%	$179.9784	$179.98	$180.00	$180.00
7 purchase totals =	$917.91		$999.7766	$999.78	$999.80	$999.80