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	$171.33	10.522%	$189.3573	$189.36	$189.35	$189.40
Purchase #2	$40.35	12.209%	$45.2763	$45.28	$45.30	$45.30
Purchase #3	$79.98	12.544%	$90.0127	$90.01	$90.00	$90.00
Purchase #4	$20.61	4.835%	$21.6065	$21.61	$21.60	$21.60
Purchase #5	$169.87	10.374%	$187.4923	$187.49	$187.50	$187.50
Purchase #6	$190.85	7.697%	$205.5397	$205.54	$205.55	$205.50
Purchase #7	$102.39	10.814%	$113.4625	$113.46	$113.45	$113.50
7 purchase totals =	$775.38		$852.7473	$852.75	$852.75	$852.80