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	$72.59	10.828%	$80.45	$80.45	$80.45	$80.50
Purchase #2	$205.63	12.713%	$231.7717	$231.77	$231.75	$231.80
Purchase #3	$122.59	11.331%	$136.4807	$136.48	$136.50	$136.50
Purchase #4	$189.26	8.556%	$205.4531	$205.45	$205.45	$205.50
Purchase #5	$238.45	9.450%	$260.9835	$260.98	$261.00	$261.00
Purchase #6	$88.54	12.697%	$99.7819	$99.78	$99.80	$99.80
Purchase #7	$102.35	9.678%	$112.2554	$112.26	$112.25	$112.30
7 purchase totals =	$1,019.41		$1,127.1763	$1,127.17	$1,127.20	$1,127.40