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	$16.66	9.638%	$18.2657	$18.27	$18.25	$18.30
Purchase #2	$245.49	9.577%	$269.0006	$269.00	$269.00	$269.00
Purchase #3	$78.35	10.344%	$86.4545	$86.45	$86.45	$86.50
Purchase #4	$228.43	11.774%	$255.3253	$255.33	$255.35	$255.30
Purchase #5	$31.61	12.783%	$35.6507	$35.65	$35.65	$35.70
Purchase #6	$97.77	12.662%	$110.1496	$110.15	$110.15	$110.10
Purchase #7	$121.91	4.628%	$127.552	$127.55	$127.55	$127.60
7 purchase totals =	$820.22		$902.3984	$902.40	$902.40	$902.50