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	$126.80	10.542%	$140.1673	$140.17	$140.15	$140.20
Purchase #2	$74.39	12.113%	$83.4009	$83.40	$83.40	$83.40
Purchase #3	$74.59	5.480%	$78.6775	$78.68	$78.70	$78.70
Purchase #4	$56.53	10.791%	$62.6302	$62.63	$62.65	$62.60
Purchase #5	$113.79	13.298%	$128.9218	$128.92	$128.90	$128.90
Purchase #6	$163.93	4.413%	$171.1642	$171.16	$171.15	$171.20
Purchase #7	$105.89	9.819%	$116.2873	$116.29	$116.30	$116.30
7 purchase totals =	$715.92		$781.2492	$781.25	$781.25	$781.30