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	$119.62	6.596%	$127.5101	$127.51	$127.50	$127.50
Purchase #2	$36.48	5.220%	$38.3843	$38.38	$38.40	$38.40
Purchase #3	$6.77	10.461%	$7.4782	$7.48	$7.50	$7.50
Purchase #4	$77.32	4.791%	$81.0244	$81.02	$81.00	$81.00
Purchase #5	$128.47	7.223%	$137.7494	$137.75	$137.75	$137.70
Purchase #6	$206.36	10.460%	$227.9453	$227.95	$227.95	$227.90
Purchase #7	$203.78	12.505%	$229.2627	$229.26	$229.25	$229.30
7 purchase totals =	$778.80		$849.3544	$849.35	$849.35	$849.30