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	$187.94	12.550%	$211.5265	$211.53	$211.55	$211.50
Purchase #2	$55.47	6.617%	$59.1404	$59.14	$59.15	$59.10
Purchase #3	$36.28	8.863%	$39.4955	$39.50	$39.50	$39.50
Purchase #4	$73.75	9.815%	$80.9886	$80.99	$81.00	$81.00
Purchase #5	$122.36	4.453%	$127.8087	$127.81	$127.80	$127.80
Purchase #6	$72.69	11.448%	$81.0116	$81.01	$81.00	$81.00
Purchase #7	$57.94	11.480%	$64.5915	$64.59	$64.60	$64.60
7 purchase totals =	$606.43		$664.5628	$664.57	$664.60	$664.50