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	$223.57	6.858%	$238.9024	$238.90	$238.90	$238.90
Purchase #2	$228.59	5.432%	$241.007	$241.01	$241.00	$241.00
Purchase #3	$130.65	9.556%	$143.1349	$143.13	$143.15	$143.10
Purchase #4	$197.44	6.780%	$210.8264	$210.83	$210.85	$210.80
Purchase #5	$45.55	7.802%	$49.1038	$49.10	$49.10	$49.10
Purchase #6	$28.53	10.441%	$31.5088	$31.51	$31.50	$31.50
Purchase #7	$39.39	8.138%	$42.5956	$42.60	$42.60	$42.60
7 purchase totals =	$893.72		$957.0789	$957.08	$957.10	$957.00