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	$228.49	3.340%	$236.1216	$236.12	$236.10	$236.10
Purchase #2	$42.31	11.317%	$47.0982	$47.10	$47.10	$47.10
Purchase #3	$46.92	13.779%	$53.3851	$53.39	$53.40	$53.40
Purchase #4	$96.42	5.707%	$101.9227	$101.92	$101.90	$101.90
Purchase #5	$103.78	12.106%	$116.3436	$116.34	$116.35	$116.30
Purchase #6	$19.41	10.199%	$21.3896	$21.39	$21.40	$21.40
Purchase #7	$56.31	5.715%	$59.5281	$59.53	$59.55	$59.50
7 purchase totals =	$593.64		$635.7889	$635.79	$635.80	$635.70