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	$170.68	4.814%	$178.8965	$178.90	$178.90	$178.90
Purchase #2	$86.30	10.756%	$95.5824	$95.58	$95.60	$95.60
Purchase #3	$79.67	3.356%	$82.3437	$82.34	$82.35	$82.30
Purchase #4	$29.89	6.261%	$31.7614	$31.76	$31.75	$31.80
Purchase #5	$40.98	4.810%	$42.9511	$42.95	$42.95	$43.00
Purchase #6	$217.71	10.389%	$240.3279	$240.33	$240.35	$240.30
Purchase #7	$74.67	6.593%	$79.593	$79.59	$79.60	$79.60
7 purchase totals =	$699.90		$751.4560	$751.45	$751.50	$751.50