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	$170.82	5.790%	$180.7105	$180.71	$180.70	$180.70
Purchase #2	$211.74	10.650%	$234.2903	$234.29	$234.30	$234.30
Purchase #3	$164.43	9.517%	$180.0788	$180.08	$180.10	$180.10
Purchase #4	$190.64	13.291%	$215.978	$215.98	$216.00	$216.00
Purchase #5	$69.40	3.764%	$72.0122	$72.01	$72.00	$72.00
Purchase #6	$94.27	3.873%	$97.9211	$97.92	$97.90	$97.90
Purchase #7	$97.30	6.866%	$103.9806	$103.98	$104.00	$104.00
7 purchase totals =	$998.60		$1,084.9715	$1,084.97	$1,085.00	$1,085.00