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	$90.73	3.310%	$93.7332	$93.73	$93.75	$93.70
Purchase #2	$46.54	10.140%	$51.2592	$51.26	$51.25	$51.30
Purchase #3	$233.36	13.256%	$264.2942	$264.29	$264.30	$264.30
Purchase #4	$143.32	12.290%	$160.934	$160.93	$160.95	$160.90
Purchase #5	$96.74	13.535%	$109.8338	$109.83	$109.85	$109.80
Purchase #6	$182.50	9.855%	$200.4854	$200.49	$200.50	$200.50
Purchase #7	$212.38	3.508%	$219.8303	$219.83	$219.85	$219.80
7 purchase totals =	$1,005.57		$1,100.3701	$1,100.36	$1,100.45	$1,100.30