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	$123.49	12.682%	$139.151	$139.15	$139.15	$139.20
Purchase #2	$232.63	3.204%	$240.0835	$240.08	$240.10	$240.10
Purchase #3	$156.35	11.732%	$174.693	$174.69	$174.70	$174.70
Purchase #4	$168.75	9.301%	$184.4454	$184.45	$184.45	$184.40
Purchase #5	$103.67	9.872%	$113.9043	$113.90	$113.90	$113.90
Purchase #6	$121.82	12.135%	$136.6029	$136.60	$136.60	$136.60
Purchase #7	$101.67	3.771%	$105.504	$105.50	$105.50	$105.50
7 purchase totals =	$1,008.38		$1,094.3841	$1,094.37	$1,094.40	$1,094.40