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	$187.89	12.488%	$211.3537	$211.35	$211.35	$211.40
Purchase #2	$20.56	12.105%	$23.0488	$23.05	$23.05	$23.00
Purchase #3	$136.34	10.394%	$150.5112	$150.51	$150.50	$150.50
Purchase #4	$91.59	13.558%	$104.0078	$104.01	$104.00	$104.00
Purchase #5	$58.98	3.255%	$60.8998	$60.90	$60.90	$60.90
Purchase #6	$34.95	7.383%	$37.5304	$37.53	$37.55	$37.50
Purchase #7	$136.78	4.665%	$143.1608	$143.16	$143.15	$143.20
7 purchase totals =	$667.09		$730.5125	$730.51	$730.50	$730.50