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	$128.73	8.687%	$139.9128	$139.91	$139.90	$139.90
Purchase #2	$82.46	12.673%	$92.9102	$92.91	$92.90	$92.90
Purchase #3	$174.59	9.196%	$190.6453	$190.65	$190.65	$190.60
Purchase #4	$89.29	4.316%	$93.1438	$93.14	$93.15	$93.10
Purchase #5	$106.55	12.326%	$119.6834	$119.68	$119.70	$119.70
Purchase #6	$22.51	13.254%	$25.4935	$25.49	$25.50	$25.50
Purchase #7	$121.45	13.473%	$137.813	$137.81	$137.80	$137.80
7 purchase totals =	$725.58		$799.6020	$799.59	$799.60	$799.50