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	$236.27	8.467%	$256.275	$256.28	$256.30	$256.30
Purchase #2	$85.25	10.692%	$94.3649	$94.36	$94.35	$94.40
Purchase #3	$124.91	12.325%	$140.3052	$140.31	$140.30	$140.30
Purchase #4	$71.42	9.814%	$78.4292	$78.43	$78.45	$78.40
Purchase #5	$30.70	7.794%	$33.0928	$33.09	$33.10	$33.10
Purchase #6	$24.90	11.126%	$27.6704	$27.67	$27.65	$27.70
Purchase #7	$21.91	10.585%	$24.2292	$24.23	$24.25	$24.20
7 purchase totals =	$595.36		$654.3667	$654.37	$654.40	$654.40