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	$115.81	13.458%	$131.3957	$131.40	$131.40	$131.40
Purchase #2	$114.46	12.512%	$128.7812	$128.78	$128.80	$128.80
Purchase #3	$203.77	13.815%	$231.9208	$231.92	$231.90	$231.90
Purchase #4	$116.92	4.860%	$122.6023	$122.60	$122.60	$122.60
Purchase #5	$88.36	9.266%	$96.5474	$96.55	$96.55	$96.50
Purchase #6	$105.79	6.642%	$112.8166	$112.82	$112.80	$112.80
Purchase #7	$181.87	8.127%	$196.6506	$196.65	$196.65	$196.70
7 purchase totals =	$926.98		$1,020.7146	$1,020.72	$1,020.70	$1,020.70