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	$53.58	10.791%	$59.3618	$59.36	$59.35	$59.40
Purchase #2	$217.69	8.444%	$236.0717	$236.07	$236.05	$236.10
Purchase #3	$88.89	13.741%	$101.1044	$101.10	$101.10	$101.10
Purchase #4	$186.26	10.542%	$205.8955	$205.90	$205.90	$205.90
Purchase #5	$180.49	12.628%	$203.2823	$203.28	$203.30	$203.30
Purchase #6	$174.89	8.320%	$189.4408	$189.44	$189.45	$189.40
Purchase #7	$82.86	9.217%	$90.4972	$90.50	$90.50	$90.50
7 purchase totals =	$984.66		$1,085.6537	$1,085.65	$1,085.65	$1,085.70