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	$59.54	11.828%	$66.5824	$66.58	$66.60	$66.60
Purchase #2	$42.27	13.320%	$47.9004	$47.90	$47.90	$47.90
Purchase #3	$142.56	13.405%	$161.6702	$161.67	$161.65	$161.70
Purchase #4	$6.99	12.784%	$7.8836	$7.88	$7.90	$7.90
Purchase #5	$136.27	3.555%	$141.1144	$141.11	$141.10	$141.10
Purchase #6	$219.63	10.413%	$242.5001	$242.50	$242.50	$242.50
Purchase #7	$177.59	6.321%	$188.8155	$188.82	$188.80	$188.80
7 purchase totals =	$784.85		$856.4666	$856.46	$856.45	$856.50