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	$37.28	8.706%	$40.5256	$40.53	$40.55	$40.50
Purchase #2	$66.38	5.577%	$70.082	$70.08	$70.10	$70.10
Purchase #3	$81.45	5.534%	$85.9574	$85.96	$85.95	$86.00
Purchase #4	$42.38	7.450%	$45.5373	$45.54	$45.55	$45.50
Purchase #5	$229.78	9.141%	$250.7842	$250.78	$250.80	$250.80
Purchase #6	$28.26	4.515%	$29.5359	$29.54	$29.55	$29.50
Purchase #7	$216.25	13.612%	$245.686	$245.69	$245.70	$245.70
7 purchase totals =	$701.78		$768.1084	$768.12	$768.20	$768.10