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	$99.68	5.654%	$105.3159	$105.32	$105.30	$105.30
Purchase #2	$200.30	12.112%	$224.5603	$224.56	$224.55	$224.60
Purchase #3	$56.88	4.278%	$59.3133	$59.31	$59.30	$59.30
Purchase #4	$115.61	7.712%	$124.5258	$124.53	$124.55	$124.50
Purchase #5	$163.88	11.406%	$182.5722	$182.57	$182.55	$182.60
Purchase #6	$132.98	13.814%	$151.3499	$151.35	$151.35	$151.30
Purchase #7	$41.49	4.357%	$43.2977	$43.30	$43.30	$43.30
7 purchase totals =	$810.82		$890.9351	$890.94	$890.90	$890.90