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	$29.40	13.866%	$33.4766	$33.48	$33.50	$33.50
Purchase #2	$132.77	13.200%	$150.2956	$150.30	$150.30	$150.30
Purchase #3	$168.88	12.845%	$190.5726	$190.57	$190.55	$190.60
Purchase #4	$235.61	8.849%	$256.4591	$256.46	$256.45	$256.50
Purchase #5	$174.41	6.732%	$186.1513	$186.15	$186.15	$186.20
Purchase #6	$123.73	10.156%	$136.296	$136.30	$136.30	$136.30
Purchase #7	$38.68	6.353%	$41.1373	$41.14	$41.15	$41.10
7 purchase totals =	$903.48		$994.3885	$994.40	$994.40	$994.50