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	$75.35	9.814%	$82.7448	$82.74	$82.75	$82.70
Purchase #2	$227.64	6.305%	$241.9927	$241.99	$242.00	$242.00
Purchase #3	$72.49	7.694%	$78.0674	$78.07	$78.05	$78.10
Purchase #4	$38.88	6.685%	$41.4791	$41.48	$41.50	$41.50
Purchase #5	$59.75	9.417%	$65.3767	$65.38	$65.40	$65.40
Purchase #6	$154.67	6.369%	$164.5209	$164.52	$164.50	$164.50
Purchase #7	$137.34	3.182%	$141.7102	$141.71	$141.70	$141.70
7 purchase totals =	$766.12		$815.8918	$815.89	$815.90	$815.90