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	$99.36	10.181%	$109.4758	$109.48	$109.50	$109.50
Purchase #2	$131.78	3.437%	$136.3093	$136.31	$136.30	$136.30
Purchase #3	$104.74	11.777%	$117.0752	$117.08	$117.10	$117.10
Purchase #4	$240.30	6.775%	$256.5803	$256.58	$256.60	$256.60
Purchase #5	$121.39	12.638%	$136.7313	$136.73	$136.75	$136.70
Purchase #6	$75.59	13.113%	$85.5021	$85.50	$85.50	$85.50
Purchase #7	$104.32	8.464%	$113.1496	$113.15	$113.15	$113.10
7 purchase totals =	$877.48		$954.8236	$954.83	$954.90	$954.80