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	$76.39	3.116%	$78.7703	$78.77	$78.75	$78.80
Purchase #2	$220.47	13.323%	$249.8432	$249.84	$249.85	$249.80
Purchase #3	$49.27	3.534%	$51.0112	$51.01	$51.00	$51.00
Purchase #4	$118.33	4.377%	$123.5093	$123.51	$123.50	$123.50
Purchase #5	$238.80	4.289%	$249.0421	$249.04	$249.05	$249.00
Purchase #6	$165.58	9.570%	$181.426	$181.43	$181.45	$181.40
Purchase #7	$232.51	11.116%	$258.3558	$258.36	$258.35	$258.40
7 purchase totals =	$1,101.35		$1,191.9579	$1,191.96	$1,191.95	$1,191.90