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	$83.68	5.223%	$88.0506	$88.05	$88.05	$88.10
Purchase #2	$106.77	11.730%	$119.2941	$119.29	$119.30	$119.30
Purchase #3	$211.32	3.411%	$218.5281	$218.53	$218.55	$218.50
Purchase #4	$129.78	10.668%	$143.6249	$143.62	$143.60	$143.60
Purchase #5	$79.49	3.708%	$82.4375	$82.44	$82.45	$82.40
Purchase #6	$154.50	7.186%	$165.6024	$165.60	$165.60	$165.60
Purchase #7	$205.36	9.522%	$224.9144	$224.91	$224.90	$224.90
7 purchase totals =	$970.90		$1,042.4520	$1,042.44	$1,042.45	$1,042.40