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	3.548%	$78.0234	$78.02	$78.00	$78.00
Purchase #2	$28.98	8.757%	$31.5178	$31.52	$31.50	$31.50
Purchase #3	$133.74	11.326%	$148.8874	$148.89	$148.90	$148.90
Purchase #4	$120.82	13.362%	$136.964	$136.96	$136.95	$137.00
Purchase #5	$77.83	12.435%	$87.5082	$87.51	$87.50	$87.50
Purchase #6	$176.60	12.528%	$198.7244	$198.72	$198.70	$198.70
Purchase #7	$177.66	6.864%	$189.8546	$189.85	$189.85	$189.90
7 purchase totals =	$790.98		$871.4798	$871.47	$871.40	$871.50