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	$180.50	10.527%	$199.5012	$199.50	$199.50	$199.50
Purchase #2	$114.66	8.865%	$124.8246	$124.82	$124.80	$124.80
Purchase #3	$178.90	12.240%	$200.7974	$200.80	$200.80	$200.80
Purchase #4	$52.63	12.714%	$59.3214	$59.32	$59.30	$59.30
Purchase #5	$92.38	8.188%	$99.9441	$99.94	$99.95	$99.90
Purchase #6	$177.73	8.828%	$193.42	$193.42	$193.40	$193.40
Purchase #7	$68.38	5.682%	$72.2654	$72.27	$72.25	$72.30
7 purchase totals =	$865.18		$950.0741	$950.07	$950.00	$950.00