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	$33.34	4.606%	$34.8756	$34.88	$34.90	$34.90
Purchase #2	$128.69	13.643%	$146.2472	$146.25	$146.25	$146.20
Purchase #3	$213.74	11.633%	$238.6044	$238.60	$238.60	$238.60
Purchase #4	$73.76	9.299%	$80.6189	$80.62	$80.60	$80.60
Purchase #5	$65.46	7.281%	$70.2261	$70.23	$70.25	$70.20
Purchase #6	$156.54	5.326%	$164.8773	$164.88	$164.90	$164.90
Purchase #7	$80.45	5.800%	$85.1161	$85.12	$85.10	$85.10
7 purchase totals =	$751.98		$820.5656	$820.58	$820.60	$820.50