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	$28.67	10.586%	$31.705	$31.71	$31.70	$31.70
Purchase #2	$109.79	12.374%	$123.3754	$123.38	$123.40	$123.40
Purchase #3	$99.72	11.139%	$110.8278	$110.83	$110.85	$110.80
Purchase #4	$117.41	11.451%	$130.8546	$130.85	$130.85	$130.90
Purchase #5	$206.99	6.789%	$221.0426	$221.04	$221.05	$221.00
Purchase #6	$197.81	3.618%	$204.9668	$204.97	$204.95	$205.00
Purchase #7	$249.79	12.352%	$280.6441	$280.64	$280.65	$280.60
7 purchase totals =	$1,010.18		$1,103.4163	$1,103.42	$1,103.45	$1,103.40