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	$19.39	8.358%	$21.0106	$21.01	$21.00	$21.00
Purchase #2	$63.38	8.803%	$68.9593	$68.96	$68.95	$69.00
Purchase #3	$189.61	10.566%	$209.6442	$209.64	$209.65	$209.60
Purchase #4	$80.31	12.836%	$90.6186	$90.62	$90.60	$90.60
Purchase #5	$164.84	6.695%	$175.876	$175.88	$175.90	$175.90
Purchase #6	$37.62	7.618%	$40.4859	$40.49	$40.50	$40.50
Purchase #7	$185.37	12.590%	$208.7081	$208.71	$208.70	$208.70
7 purchase totals =	$740.52		$815.3027	$815.31	$815.30	$815.30