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	$5.90	11.192%	$6.5603	$6.56	$6.55	$6.60
Purchase #2	$208.32	6.856%	$222.6024	$222.60	$222.60	$222.60
Purchase #3	$211.92	3.269%	$218.8477	$218.85	$218.85	$218.80
Purchase #4	$201.84	3.607%	$209.1204	$209.12	$209.10	$209.10
Purchase #5	$49.89	7.449%	$53.6063	$53.61	$53.60	$53.60
Purchase #6	$126.25	6.355%	$134.2732	$134.27	$134.25	$134.30
Purchase #7	$139.78	9.140%	$152.5559	$152.56	$152.55	$152.60
7 purchase totals =	$943.90		$997.5662	$997.57	$997.50	$997.60