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	$82.69	9.346%	$90.4182	$90.42	$90.40	$90.40
Purchase #2	$81.96	10.770%	$90.7871	$90.79	$90.80	$90.80
Purchase #3	$113.36	10.546%	$125.3149	$125.31	$125.30	$125.30
Purchase #4	$66.52	9.407%	$72.7775	$72.78	$72.80	$72.80
Purchase #5	$225.30	8.787%	$245.0971	$245.10	$245.10	$245.10
Purchase #6	$174.81	12.668%	$196.9549	$196.95	$196.95	$197.00
Purchase #7	$101.29	12.273%	$113.7213	$113.72	$113.70	$113.70
7 purchase totals =	$845.93		$935.0710	$935.07	$935.05	$935.10