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	$73.96	9.172%	$80.7436	$80.74	$80.75	$80.70
Purchase #2	$185.56	10.476%	$204.9993	$205.00	$205.00	$205.00
Purchase #3	$43.90	7.262%	$47.088	$47.09	$47.10	$47.10
Purchase #4	$66.44	8.190%	$71.8814	$71.88	$71.90	$71.90
Purchase #5	$100.75	10.506%	$111.3348	$111.33	$111.35	$111.30
Purchase #6	$195.27	7.219%	$209.3665	$209.37	$209.35	$209.40
Purchase #7	$240.93	13.252%	$272.858	$272.86	$272.85	$272.90
7 purchase totals =	$906.81		$998.2716	$998.27	$998.30	$998.30