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	$118.89	10.572%	$131.4591	$131.46	$131.45	$131.50
Purchase #2	$77.71	9.476%	$85.0738	$85.07	$85.05	$85.10
Purchase #3	$123.51	13.348%	$139.9961	$140.00	$140.00	$140.00
Purchase #4	$124.98	3.278%	$129.0768	$129.08	$129.10	$129.10
Purchase #5	$136.73	13.641%	$155.3813	$155.38	$155.40	$155.40
Purchase #6	$126.90	9.439%	$138.8781	$138.88	$138.90	$138.90
Purchase #7	$80.77	7.137%	$86.5346	$86.53	$86.55	$86.50
7 purchase totals =	$789.49		$866.3998	$866.40	$866.45	$866.50