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	$111.30	13.208%	$126.0005	$126.00	$126.00	$126.00
Purchase #2	$145.36	6.407%	$154.6732	$154.67	$154.65	$154.70
Purchase #3	$81.39	3.119%	$83.9286	$83.93	$83.95	$83.90
Purchase #4	$195.86	7.645%	$210.8335	$210.83	$210.85	$210.80
Purchase #5	$137.46	4.590%	$143.7694	$143.77	$143.75	$143.80
Purchase #6	$31.66	13.194%	$35.8372	$35.84	$35.85	$35.80
Purchase #7	$156.29	9.746%	$171.522	$171.52	$171.50	$171.50
7 purchase totals =	$859.32		$926.5644	$926.56	$926.55	$926.50