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	$202.98	4.234%	$211.5742	$211.57	$211.55	$211.60
Purchase #2	$168.73	10.273%	$186.0636	$186.06	$186.05	$186.10
Purchase #3	$248.28	12.534%	$279.3994	$279.40	$279.40	$279.40
Purchase #4	$127.44	10.843%	$141.2583	$141.26	$141.25	$141.30
Purchase #5	$99.84	13.520%	$113.3384	$113.34	$113.35	$113.30
Purchase #6	$133.89	9.455%	$146.5493	$146.55	$146.55	$146.50
Purchase #7	$99.35	3.274%	$102.6027	$102.60	$102.60	$102.60
7 purchase totals =	$1,080.51		$1,180.7859	$1,180.78	$1,180.75	$1,180.80