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	$35.58	13.302%	$40.3129	$40.31	$40.30	$40.30
Purchase #2	$79.90	7.636%	$86.0012	$86.00	$86.00	$86.00
Purchase #3	$78.96	13.399%	$89.5399	$89.54	$89.55	$89.50
Purchase #4	$158.80	11.445%	$176.9747	$176.97	$176.95	$177.00
Purchase #5	$247.93	3.216%	$255.9034	$255.90	$255.90	$255.90
Purchase #6	$238.53	10.683%	$264.0122	$264.01	$264.00	$264.00
Purchase #7	$239.27	4.214%	$249.3528	$249.35	$249.35	$249.40
7 purchase totals =	$1,078.97		$1,162.0971	$1,162.08	$1,162.05	$1,162.10