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	$236.80	12.766%	$267.0299	$267.03	$267.05	$267.00
Purchase #2	$25.94	7.126%	$27.7885	$27.79	$27.80	$27.80
Purchase #3	$153.77	4.414%	$160.5574	$160.56	$160.55	$160.60
Purchase #4	$147.99	11.757%	$165.3892	$165.39	$165.40	$165.40
Purchase #5	$87.77	3.640%	$90.9648	$90.96	$90.95	$91.00
Purchase #6	$224.64	11.393%	$250.2332	$250.23	$250.25	$250.20
Purchase #7	$174.41	4.129%	$181.6114	$181.61	$181.60	$181.60
7 purchase totals =	$1,051.32		$1,143.5744	$1,143.57	$1,143.60	$1,143.60