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	$131.79	6.540%	$140.4091	$140.41	$140.40	$140.40
Purchase #2	$53.69	10.564%	$59.3618	$59.36	$59.35	$59.40
Purchase #3	$100.70	3.357%	$104.0805	$104.08	$104.10	$104.10
Purchase #4	$241.99	5.362%	$254.9655	$254.97	$254.95	$255.00
Purchase #5	$77.74	6.642%	$82.9035	$82.90	$82.90	$82.90
Purchase #6	$131.65	6.758%	$140.5469	$140.55	$140.55	$140.50
Purchase #7	$6.60	10.351%	$7.2832	$7.28	$7.30	$7.30
7 purchase totals =	$744.16		$789.5505	$789.55	$789.55	$789.60